Need to run git cache exists in a directory we know for sure that exists

gclient_scm.py

Index: gclient_scm.py
diff --git a/gclient_scm.py b/gclient_scm.py
index 238122fce653903fd38b9ab28d93d1030dc0fed7..af48b5f7f33b5984667abe2e4887f9f224e59737 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -685,7 +685,7 @@ class GitWrapper(SCMWrapper):
               ['--shallow', '--cache-dir', self.cache_dir, url],
               options, cwd=self._root_dir, retry=True)
     return self._Run(['cache', 'exists', '--cache-dir', self.cache_dir, url],
-                     options).strip()
+                     options, cwd=self._root_dir, ).strip()
 
   def _Clone(self, revision, url, options):
     """Clone a git repository from the given URL.