Update CONTRIBUTING.md

minor wording fix
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 4a7b952..204bba5 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -48,5 +48,5 @@
 ----------
 
 We love to hear from you. If you want to work on something or have
-questions / complaints please reach out to us by at
+questions / feedback, please reach out to us at
 https://groups.google.com/forum/#!forum/predictionio-dev