Release: Updates to v2.0.0-beta.

package.json

 {
   "name": "node-sass",
-  "version": "2.0.0-alpha",
-  "libsass": "3.1.0-alpha",
+  "version": "2.0.0-beta",
+  "libsass": "3.1.0-beta",
   "description": "Wrapper around libsass",
   "license": "MIT",
   "homepage": "https://github.com/sass/node-sass",