Upgraded xtend to 2.1.1.
Upgraded xtend to 2.1.1.

The object-keys package to which the old xtend is depending gives a bad
deprecation warning. Not really nice for a cool package.

timkuijsten/levelup,roppa/levelup,toddself/levelup,roppa/levelup,toddself/levelup,timkuijsten/levelup,JTKnox91/levelup,djchie/levelup,lastguest/levelup,JTKnox91/levelup,djchie/levelup,Level/levelup,lastguest/levelup