Fixes consistency when using OAuth2 bearer tokens.
We should be using an Authorization header value of: "Authorization: bearer OAUTH-TOKEN", like we do elsewhere in the docs.
Use OAUTH-TOKEN rather than just TOKEN, just for consistency.
Standardise on token because of other documentation and blog posts which use token.
Merge pull request #288 from github/jdennes-auth-token-consistency

Better OAuth2 token consistency.