Travis-CI build matrix for cross-building

Author: guilgaly

.ci_scripts/validate.sh

@@ -4,7 +4,7 @@ set -e
 
 echo "[INFO] Check the source format"
 
-sbt scalafmt test:scalafmt > /dev/null
+sbt ++$TRAVIS_SCALA_VERSION scalafmt test:scalafmt > /dev/null
 git diff --exit-code || (cat >> /dev/stdout <<EOF
 [ERROR] Scalafmt check failed, see differences above.
 To fix, format your sources using sbt scalafmt test:scalafmt before submitting a pull request.
@@ -15,4 +15,4 @@ false
 
 echo "[INFO] Running tests" >> /dev/stdout
 
-sbt clean +test
+sbt ++$TRAVIS_SCALA_VERSION test

.travis.yml

@@ -1,5 +1,8 @@
 sudo: false
 language: scala
+scala:
+  - 2.12.7
+  - 2.11.12
 jdk:
   - oraclejdk8
 cache: