TBR: syncslides: ignore android/gen directory.

Change-Id: I522f7a906118401659159dc3414edda4303336d4
diff --git a/android/.gitignore b/android/.gitignore
index d5e1648..f7a63f4 100644
--- a/android/.gitignore
+++ b/android/.gitignore
@@ -7,3 +7,4 @@
 /captures
 .idea/
 *.iml
+/gen/