Override gradle invocation to avoid install.

Capstan · Capstan · commit 357a8fb809e0 · 2019-09-30T15:34:08.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,4 +2,7 @@ language: java
 jdk:
   - openjdk8
   - openjdk11
+install: {}
+script:
+  - ./gradlew assemble check
 
