Added the path to the executable for npm rc 1.0.x

This should work in older versions of npm as well. Without the bin reference in npm 1.0.x it won't get installed into a PATH. I just upgraded npm this evening and adding this in and running npm link seems to work fine.

package.json

@@ -12,7 +12,8 @@
     "type": "MIT",
     "url": "http://www.opensource.org/licenses/mit-license.php"
   }],
-  "main": "./packages/jshint/jshint",
+  "bin": { "jshint": "./bin/jshint" },
+  "main": "packages/jshint/jshint",
   "files": [
     "packages/jshint/README.markdown",
     "packages/jshint/jshint.js",