Fixes the AMD detection

`typeof define` returns `function` if it is available.
`if ( typeof define === "object“ ... )` is always `false`.
We simply have to check for `if (typeof define === "function" ... )` to
fix this.
Fixes w.picturefill() is `undefined`

`w.picturefill();` is `undefined` if picturefill is exposed via AMD as
an anonymous module. Should be `picturefill();`
Build dist
Merge branch 'fix-amd-support' of https://github.com/andreruffert/picturefill into andreruffert-fix-amd-support

Conflicts:
	dist/picturefill.js
	dist/picturefill.min.js
Merge branch 'andreruffert-fix-amd-support'