feat: remove dependency on coffee-script

Karma never used coffee-script directly, it's just so that people can write config file in CoffeeScript.

Now it's only required if available. That means, if the developer wants to use CoffeeScript syntax, he has to install coffee-script on his own (put it in package.json).

package.json

@@ -117,7 +117,6 @@
     "minimatch": "~0.2",
     "http-proxy": "~0.10",
     "optimist": "~0.6.0",
-    "coffee-script": "~1.6",
     "rimraf": "~2.2.5",
     "q": "~0.9.7",
     "colors": "~0.6.2",
@@ -167,7 +166,8 @@
     "karma-html2js-preprocessor": "*",
     "karma-browserstack-launcher": "*",
     "LiveScript": "~1.2.0",
-    "coffee-errors": "~0.8.6"
+    "coffee-errors": "~0.8.6",
+    "coffee-script": "~1.6"
   },
   "main": "./lib/index",
   "bin": {},