Do not build source maps when compiling coffee scripts.

Since we do not ship coffee script sources and source map files in final
build, the source maps generated here actually have no use, and would
cause lots of networking erros since each compiled .js would try to load
their corresponding source map file.

This doesn't affect dev mode because it has its own way to generate
source maps on the fly.

Closes #1836.

build/Gruntfile.coffee

@@ -68,8 +68,6 @@ module.exports = (grunt) ->
     installDir = process.env.INSTALL_PREFIX ? '/usr/local'
 
   coffeeConfig =
-    options:
-      sourceMap: true
     glob_to_multiple:
       expand: true
       src: [