Add Travis-CI caching rule to config

Author: patrickfav

.travis.yml

@@ -46,6 +46,10 @@ deploy:
       branch: master
       tags: true
 
+cache:
+  directories:
+    - $HOME/.m2
+
 notifications:
   slack:
     secure: "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"