Update description of Snippets API, create and update methods
Update description of Snippets API, create and update methods

Currently, the field used to fill the contents is called "code".
Also "visibility" is now required.

stoplightio/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq