Add preview script

package.json

@@ -18,7 +18,8 @@
     "copy-dist-to-examples": "cp dist/nodesphere.js examples/",
     "publish:gh-pages": "gh-pages --dist examples --message 'Update gh-pages [ci skip]'",
     "publish:gh-pages:notify": "echo http://nodesphere.github.io/nodesphere",
-    "ipfs": "open https://ipfs.io/ipfs/`~/gocode/bin/ipfs add -r -q examples | tail -n 1`"
+    "ipfs": "open https://ipfs.io/ipfs/`~/gocode/bin/ipfs add -r -q examples | tail -n 1`",
+    "preview": "http-server examples -c-1 -p 1234"
   },
   "author": "Harlan T Wood (https://github.com/harlantwood)",
   "contributors": [