bower.json: rm moot `version` field

Per https://github.com/bower/bower.json-spec/commit/a325da3d79baab018c572d75dc1781b12322f6cd

bower.json

 {
   "name": "bootstrap",
   "description": "The most popular front-end framework for developing responsive, mobile first projects on the web.",
-  "version": "3.3.4",
   "keywords": [
     "css",
     "js",