Increase git depth, since there maybe a lag from when we trigger a build to other changes getting checked into the repo. In which case git checkout on a commit id (after cloning with the extra changes) fails with "fatal: reference is not a tree"

PiperOrigin-RevId: 239673455

Author: afrozenator

.travis.yml

@@ -2,7 +2,7 @@ sudo: required
 language: python
 cache: pip
 git:
-  depth: 1
+  depth: 3
   quiet: true
 services:
   - docker