Add cache to Travis

Signed-off-by: Jadon Fowler <[email protected]>

.travis.yml

@@ -10,5 +10,16 @@ jdk:
 scala:
   - 2.12.6
 
+# Caching taken from https://www.scala-sbt.org/1.0/docs/Travis-CI-with-sbt.html#Caching
+cache:
+  directories:
+    - $HOME/.ivy2/cache
+    - $HOME/.sbt
+
+before_cache:
+  # Cleanup the cached directories to avoid unnecessary cache updates
+  - find $HOME/.ivy2/cache -name "ivydata-*.properties" -print -delete
+  - find $HOME/.sbt        -name "*.lock"               -print -delete
+
 script:
   - sbt ++$TRAVIS_SCALA_VERSION compile