Update api.rb

I'm getting a syntax error with the colon.
Specify gem platform and required ruby >= 2.0
Fetch Achievements game_id and gamertag switched

It kept throwing an error, so this is a futile attempt at trying
something new. I'm desperate.
Rename parameter for the API

Despite all the documentation I can find, using `gameid` consistently results in 

    ArgumentError: The gameid supplied was not valid.

`titleid` looks to be the older param name, but it still works.
gameid now titleid

Gem must be using v1.0 of the API, which had titleid. Thanks to
bscofield (my hero!).
Upgrade api to v2.0
Merge branch 'patch-1' of https://github.com/ashleybaxter/xbox_leaders into ashleybaxter-patch-1
Fix specs and misc. changes for api v2.0
merging with upstream
Merge branch 'master', remote-tracking branch 'upstream/master'