### What is this PR for?
This PR will fix [ZEPPELIN-813](https://issues.apache.org/jira/browse/ZEPPELIN-813).
I'm not sure what environment exactly generate this errors. I saw the below error in OS X 10.11.3
and ruby 2.3.0.
```
$ bundle exec jekyll serve --watch
/Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/user_interaction.rb:328: warning: constant ::TimeoutError is deprecated
/Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/runner.rb:365:in `block in require_program': program version required (Commander::Runner::CommandError)
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/runner.rb:364:in `each'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/runner.rb:364:in `require_program'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/runner.rb:52:in `run!'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/delegates.rb:7:in `run!'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/commander-4.1.5/lib/commander/import.rb:10:in `block in <top (required)>'
/Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/safe_yaml-0.9.7/lib/safe_yaml/syck_node_monkeypatch.rb:42:in `<top (required)>': uninitialized constant Syck (NameError)
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/safe_yaml-0.9.7/lib/safe_yaml.rb:200:in `require'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/safe_yaml-0.9.7/lib/safe_yaml.rb:200:in `<module:YAML>'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/safe_yaml-0.9.7/lib/safe_yaml.rb:132:in `<top (required)>'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/jekyll-1.3.0/lib/jekyll.rb:21:in `require'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/jekyll-1.3.0/lib/jekyll.rb:21:in `<top (required)>'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/jekyll-1.3.0/bin/jekyll:7:in `require'
from /Users/cyhsutw/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/jekyll-1.3.0/bin/jekyll:7:in `<top (required)>'
from /Users/cyhsutw/.rbenv/versions/2.3.0/bin/jekyll:23:in `load'
from /Users/cyhsutw/.rbenv/versions/2.3.0/bin/jekyll:23:in `<main>'
```
Maybe this error will be gone with `bundle update`. But it would be better we set `safe_yaml` version for the other users. So I just updated `safe_yaml` version from `0.9.7` to `1.0.4` in `Gemfile.lock` manually. And confirmed that there are no compatibility issues with ruby version `2.3.0`(latest stable version), `2.2.1`, `2.1.1` and `2.0.0`(this version is no longer maintained by ruby).
I also updated `docs/README.md` since we need ruby version higher than `2.0.0` not `1.9.3`. Please see [here](https://help.github.com/articles/setting-up-your-github-pages-site-locally-with-jekyll/#requirements).
### What type of PR is it?
Bug Fix & Documentation
### What is the Jira issue?
[ZEPPELIN-813](https://issues.apache.org/jira/browse/ZEPPELIN-813)
### How should this be tested?
###### 1. Apply this patch
```
$ cd docs
$ bundle install
```
If you already installed dependencies before, you need
```
$ bundle update safe_yaml
```
###### 2. Check what version of `safe_yaml` is installed -> `1.0.4` should be installed. Then
```
$ bundle exec jekyll serve --watch
```
It should be run with no issues.
### Questions:
* Does the licenses files need update? no
* Is there breaking changes for older versions? no
* Does this needs documentation? no
Author: AhyoungRyu <fbdkdud93@hanmail.net>
Closes#1167 from AhyoungRyu/ZEPPELIN-813 and squashes the following commits:
458957d [AhyoungRyu] Add a newline
9cf8b42 [AhyoungRyu] Update docs/README.md
a2fd980 [AhyoungRyu] Update safe_yaml version 0.9.7 -> 1.0.4
#407 addressed https://issues.apache.org/jira/browse/ZEPPELIN-406 and merged into branch-0.5.5
This PR applies it to the master branch
Author: Lee moon soo <moon@apache.org>
Closes#424 from Leemoonsoo/ZEPPELIN-406-master and squashes the following commits:
64b6550 [Lee moon soo] Add apache header and inline json message example into doc
ba72645 [Lee moon soo] ZEPPELIN-406 Handle license issue found in 0.5.5-incubating rc2
Details at the [ZEPPELIN-279](https://issues.apache.org/jira/browse/ZEPPELIN-279)
Author: Alexander Bezzubov <bzz@apache.org>
Closes#282 from bzz/ZEPPELIN-279-move-docs-to-master and squashes the following commits:
16d2cd0 [Alexander Bezzubov] ZEPPELIN-279: updating refs to new /docs location
a051a35 [Alexander Bezzubov] ZEPPELIN-279: moving website gh-pages -> master:/docs
