azure/gitLab/travis: Add pygit2 as a dependency for tests

This lets patman run all of its tests, rather than skipping quite a few.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/.travis.yml b/.travis.yml
index cb48ff3..69829fc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -26,6 +26,7 @@
     - python3-sphinx
     - python3-virtualenv
     - python3-pip
+    - python3-pygit2
     - swig
     - libpython-dev
     - iasl