Configure Travis CI to cache dependencies

Author: jonas

.travis.yml

@@ -15,3 +15,14 @@ matrix:
   - env: TEST_ENV=ubuntu-18.04-llvm-dev
   - env: TEST_ENV=ubuntu-18.04-llvm-6.0
   - env: TEST_ENV=ubuntu-18.04-llvm-5.0
+
+before_cache:
+  # See https://www.scala-sbt.org/1.0/docs/Travis-CI-with-sbt.html
+  # Tricks to avoid unnecessary cache updates
+  - find $HOME/.sbt -name "*.lock" | xargs rm
+  - find $HOME/.ivy2 -name "ivydata-*.properties" | xargs rm
+
+cache:
+  directories:
+    - $HOME/.ivy2/cache
+    - $HOME/.sbt/boot