Update to buff-config ~> 0.4
Merge pull request #268 from RiotGames/sethvargo/bump_buff_config

Update to buff-config ~> 0.4
add ruby 2.1 to test matrix
update varia_model, buff-config, and buff-extensions deps
Merge pull request #273 from RiotGames/update-gem-deps

update varia_model, buff-config, and buff-extensions deps
version bump 4.0.0