use stdlib context in go-kit methods (#1454)

server/service/endpoint_decorators.go

@@ -1,9 +1,10 @@
 package service
 
 import (
+	"context"
+
 	"github.com/go-kit/kit/endpoint"
 	"github.com/kolide/kolide/server/kolide"
-	"golang.org/x/net/context"
 )
 
 type listDecoratorResponse struct {

server/service/transport_decorators.go

@@ -1,10 +1,9 @@
 package service
 
 import (
+	"context"
 	"encoding/json"
 	"net/http"
-
-	"golang.org/x/net/context"
 )
 
 func decodeNewDecoratorRequest(ctx context.Context, req *http.Request) (interface{}, error) {