.gitignore: ignore tools subdir

Change-Id: Iae755a400f8cee1ad4b64d278fc2efa0e1a96047
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>
diff --git a/.gitignore b/.gitignore
index 05735cf..ddbf130 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 /private/
 /proprietary/
 /security/
+/tools/