Update Uglify to v2

Saves 1667 bytes in zepto.min.js

make

@@ -89,7 +89,10 @@ describe_version = ->
 
 minify = (source_code) ->
   uglify = require('uglify-js')
-  ast = uglify.parser.parse(source_code)
-  ast = uglify.uglify.ast_mangle(ast)
-  ast = uglify.uglify.ast_squeeze(ast)
-  uglify.uglify.gen_code(ast)
+  compressor = uglify.Compressor()
+  ast = uglify.parse(source_code)
+  ast.figure_out_scope()
+  ast.compute_char_frequency();
+  ast.mangle_names();
+  ast = ast.transform(compressor)
+  return ast.print_to_string()

package.json

@@ -18,7 +18,7 @@
     }
   ]
   , "devDependencies": {
-      "uglify-js": "1.2.6"
+      "uglify-js": "2.4.x"
     , "express": "3.1.x"
     , "coffee-script": "1.5.x"
     , "shelljs": "0.1.x"