Travis: use ccache (#3307)

tiran · web-flow · commit 8adc73c2c1a5 · 2017-09-05T01:48:54.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -3,8 +3,10 @@ dist: trusty
 sudo: false
 group: beta
 
-# To cache doc-building dependencies.
-cache: pip
+# To cache doc-building dependencies and C compiler output.
+cache:
+    - pip
+    - ccache
 
 branches:
   only:
