Webpack support

Specify `.json` extension when requiring `package.json` as suggested by @abhishiv.

Closes #289
diff --git a/lib/nano.js b/lib/nano.js
index 19ff1f8..ab97228 100644
--- a/lib/nano.js
+++ b/lib/nano.js
@@ -758,7 +758,7 @@
  *
  * thanks for visiting! come again!
  */
-nano.version = require('../package').version;
+nano.version = require('../package.json').version;
 nano.path    = __dirname;
 
 function urlResolveFix(couchUrl, dbName) {