Having two cache: entry discards the first one, which is the one we want.

c01215fd · Arnaud Bergeron · 349de8bc · c01215fd
--- a/.travis.yml
+++ b/.travis.yml
@@ -63,5 +63,3 @@ script:

 after_failure:
  - cat /home/travis/.pip/pip.log
-
-cache: apt