Correct icon-lock and regexp

I have been testing on IE6/7 and discovered that the js fix does not work. This is as a result of "icon-locked" instead of "icon-lock" and an incorrect regexp pattern (returns "undefined" in icons - the world's least helpful error message). 

Still to confirm all "icon-" variations. Otherwise testing works in IE6 and IE7 (with @font-face correction to Icomoon.less). Will submit icomoon.less correction via pull request.