Update select2.js

Fixes unpleasant glitch where initializing select2 on select where first input option tag has non-breakable space in innerText causes selected option to be displayed as "undefined" until user changes selection. (i.e. HTML was like <option value>&nbsp;</option>, that's what Rails 3 f.select helper generate by default).
Merge pull request #2215 from pineapple-thief/pineapple-thief

Update select2.js