fix git-try broken by CheckCall return type change

Review URL: http://codereview.chromium.org/561001

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@37750 0039d316-1c4b-4281-b951-d872f2087c98

git-try

@@ -30,7 +30,7 @@ def GetRietveldPatchsetNumber():
 
 def GetRietveldServerUrl():
   return GIT.Capture(
-      ['config', 'rietveld.server'], error_ok=True).strip()
+      ['config', 'rietveld.server'], error_ok=True)[0].strip()
 
 
 if __name__ == '__main__':