add travis caching

.travis.yml

@@ -3,3 +3,13 @@ language: scala
 jdk: oraclejdk8
 script:
 - sbt ";^test ;^scripted"
+
+before_cache:
+  # Cleanup the cached directories to avoid unnecessary cache updates
+  - find $HOME/.ivy2/cache -name "ivydata-*.properties" -print -delete
+  - find $HOME/.sbt        -name "*.lock"               -print -delete
+
+cache:
+  directories:
+    - $HOME/.ivy2/cache
+    - $HOME/.sbt