Don't hardcode git directory path.

The git path is based on the git version, so it might change whenever git is
updated. Run git.bat instead, since that's updated with new git installs and
should always point to the right path.

Review URL: https://codereview.chromium.org/173393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@252299 0039d316-1c4b-4281-b951-d872f2087c98

fetch.py

@@ -79,7 +79,7 @@ class GitCheckout(Checkout):
 
   def run_git(self, *cmd, **kwargs):
     if sys.platform == 'win32' and not spawn.find_executable('git'):
-      git_path = os.path.join(SCRIPT_PATH, 'git-1.8.0_bin', 'bin', 'git.exe')
+      git_path = os.path.join(SCRIPT_PATH, 'git.bat')
     else:
       git_path = 'git'
     return self.run((git_path,) + cmd, **kwargs)