Use https in CONTRIBUTING.md
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 1731176..a17ce73 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -33,7 +33,7 @@
Before making a pull request please attempt to run `mvn verify`. If it fails and you are not sure
why, it's OK to go ahead make the pull request with a comment about the failure.
-[Git]: http://git-scm.com/
+[Git]: https://git-scm.com/
[java]: http://openjdk.java.net/
-[Maven]: http://maven.apache.org/
+[Maven]: https://maven.apache.org/
[contribute]: https://fluo.apache.org/how-to-contribute/
