[DCS] Fixes a failing test for Node.js 0.12

The test needed to be updated to not use features from ECMAScript 6.
(String.prototype.startsWith)

Author: mfulgo

test/test.document_conversion.v1-experimental.js

@@ -73,7 +73,8 @@ describe('document_conversion', function() {
 
     it('should generate a valid payload', function() {
       var req = servInstance.convert(payload, noop);
-      assert(req.uri.href.startsWith(service_options.url + convertPath));
+      var url = service_options.url + convertPath;
+      assert.equal(req.uri.href.slice(0, url.length), url);
       assert.equal(req.method, 'POST');
       assert(req.formData);
     });