add constructor

See details here http://babeljs.io/blog/2015/06/07/react-on-es6-plus/

Author: iamstarkov

linters/.eslintrc

@@ -197,6 +197,7 @@
         "mixins",
         "statics",
         "defaultProps",
+        "constructor",
         "getDefaultProps",
         "getInitialState",
         "getChildContext",