gitignore: add local.properties

  * ignore local.properties as it is specific to local configurations and
    should not get checked in into version control systems

Change-Id: Iff87ebb93c2172636649ba4ddb767e513ad255fe
diff --git a/.gitignore b/.gitignore
index 10b5ff5..8889923 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 target
 *.iml
 .idea
+local.properties