Add failing unit tests asserting old moment().lang(str) behavior
Fix moment().lang() pre 2.8 behavior
Make jscs happy
Merge pull request #1813 from ichernev/bugfix/maintain-lang-original-behavior

Fix moment().lang([key]) backwards compatibility broken in 2.8.0.
Add 2.8.1 changelog
Bump version to 2.8.1
Build 2.8.1