added a separate npm-specific main file

dist/js/npm.js

+require('../../js/transition')
+require('../../js/alert')
+require('../../js/button')
+require('../../js/carousel')
+require('../../js/collapse')
+require('../../js/dropdown')
+require('../../js/modal')
+require('../../js/tooltip')
+require('../../js/popover')
+require('../../js/scrollspy')
+require('../../js/tab')
+require('../../js/affix')

index.js

-module.exports = __dirname;

package.json

@@ -18,7 +18,7 @@
   },
   "style": "dist/css/bootstrap.css",
   "less": "less/bootstrap.less",
-  "main": "./index.js",
+  "main": "./dist/js/npm",
   "repository": {
     "type": "git",
     "url": "https://github.com/twbs/bootstrap.git"