Update the scripted Gradle Wrapper command-line to clean build artifacts, refresh dependencies and run as a non-daemon process.

.travis.yml

@@ -1,15 +1,14 @@
 language: java
 
-os:
+jdk: oraclejdk8
-  - linux
 
-jdk:
+os: linux
-  - oraclejdk8
 
-script: ./gradlew build
+script: ./gradlew --refresh-dependencies --no-daemon clean build
 
 before_cache:
   - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+
 cache:
   directories:
     - $HOME/.gradle/caches/