[#422] Correct misspelling.

Author: monkpow

lib/as.js

@@ -12,7 +12,7 @@ function asBuffer(body, options) {
   } else if (typeof body === 'object') {
     ret = new Buffer(JSON.stringify(body), options.reqBodyEncoding);
   } else if (typeof body === 'string') {
-    ret = new Buffer(body, options.reqBodyEncodeing);
+    ret = new Buffer(body, options.reqBodyEncoding);
   }
   return ret;
 }