Fix showing default help (from index.md)

rosen-vladimirov · rosen-vladimirov · commit 54861b996f10 · 2017-11-09T11:04:09.000+02:00
In case user executes:
- `tns help` - we should show the default index.html help with all commands
- `tns --help` - we should show the default command line help generated from index.md file with all commands

This has been broken during changing html-help-service to help-service.
Fix the default behavior and add tests for it.
diff --git a/lib/common b/lib/common
@@ -1 +1 @@
-Subproject commit c80e999c7009dd9e649484cd3230b6da1eba45a2
+Subproject commit df4b878e824694391313552b49a7a7490e65138e
