Use application/javascript for JSON content type

At the moment riak doesn't seem to recognize or
parse items with the content type application/json
in map functions - only application/javascript.
As a follow on, we need to recognize and set it
so we can use it for data storage.

lib/riak.js

@@ -39,7 +39,7 @@ Client.prototype.store = function(bucket, key, data, params) {
 
     switch (params && params.type) {
       case "json":
-        headers['content-type'] = "application/json";
+        headers['content-type'] = "application/javascript";
         data = JSON.stringify(data);
         break;
 
@@ -125,7 +125,8 @@ Client.prototype.makeRequest = function(method, url, headers, data) {
 
       // don't try to json parse a response if there's no content
       if (response.statusCode != 204
-          && response.headers['content-type'] == 'application/json'
+          && (response.headers['content-type'] == 'application/json' ||
+              response.headers['content-type'] == 'application/javascript')
           && Number(response.headers['content-length'])) {
         resp.data = JSON.parse(body);
       }