Add a changelog entry for rspec#1503

Closes rspec#1403

Author: Sam Phippen

Changelog.md

@@ -1,6 +1,11 @@
-### 3.4.1 Development
+### 3.5.0 Development
 [Full Changelog](http://github.com/rspec/rspec-rails/compare/v3.4.0...master)
 
+Enhancements:
+
+* Add a `---singularize` option for the feature spec generator (Felicity McCabe,
+  #1503)
+
 Bug fixes:
 
 * Make it possible to write nested specs within helper specs on classes that are