fix(cli): Use bin field in package.json

Closes #1351

Author: SimenB

package.json

@@ -227,7 +227,7 @@
     "which": "~1.0"
   },
   "main": "./lib/index",
-  "bin": {},
+  "bin": { "karma": "./bin/karma" },
   "engines": {
     "node":  ">=0.8 <=0.12",
     "iojs": "~1"