svn of depot_tools is going away, migrate to git. (#1211)

for some reason we were still using the svn for travis here, but git for everything else...
diff --git a/.travis.yml b/.travis.yml
index a1b19da..563b72b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,7 @@
   - sudo sh -c 'echo "image/webp webp" >> /etc/mime.types'
   - mkdir -p ~/bin
   - cd ~/bin
-  - svn co https://src.chromium.org/svn/trunk/tools/depot_tools 2>&1 > /dev/null
+  - git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
   - mkdir ~/mod_pagespeed
   - cd ~/mod_pagespeed
   - git clone https://github.com/pagespeed/mod_pagespeed.git src