Move spotless check to separate build task

This means the tests can run in parallel of the formatting changes.
Therefore, formatting changes would not block obtaining your test
results, which should hopefully reduce the amount of Travis builds
necessary to work on a community PR.

This is also in preparation of #1934 which requires spotless to
run on JDK11 minimum.

.travis.yml

@@ -28,6 +28,8 @@ matrix:
     env: SKIP_RELEASE=true
   - jdk: openjdk14
     env: SKIP_RELEASE=true MOCK_MAKER=mock-maker-inline
+  - jdk: openjdk11
+    script: ./gradlew spotlessCheck
 
 branches:
   #Don't build tags
@@ -44,7 +46,7 @@ script:
   # We are using && below on purpose
   # ciPerformRelease must run only when the entire build has completed
   # This guarantees that no release steps are executed when the build or tests fail
-  - ./gradlew spotlessCheck && ./gradlew build idea -s && ./gradlew checkReproducibility && ./gradlew ciPerformRelease
+  - ./gradlew build idea -s && ./gradlew checkReproducibility && ./gradlew ciPerformRelease
 
 after_success:
   #Generates coverage report: