use caching as described in https://www.scala-sbt.org/1.0/docs/Travis-CI-with-sbt.html

Author: jtjeferreira

.travis.yml

@@ -1,4 +1,18 @@
+# Use container-based infrastructure
+sudo: false
+
 language: scala
 scala:
    - 2.11.12
    - 2.12.4
+   
+# These directories are cached to S3 at the end of the build
+cache:
+  directories:
+    - $HOME/.ivy2/cache
+    - $HOME/.sbt/boot/
+
+before_cache:
+  # Tricks to avoid unnecessary cache updates
+  - find $HOME/.sbt -name "*.lock" | xargs rm
+  - find $HOME/.ivy2 -name "ivydata-*.properties" | xargs rm