adding travis file

.travis.yml

+language: java
+
+jdk:
+  - oraclejdk8
+  - openjdk8
+
+script:
+  - jdk_switcher use oraclejdk8
+  - ./gradlew assemble
+  - ./gradlew check
+  - ./gradlew test
+  - jdk_switcher use openjdk8
+  - ./gradlew assemble
+  - ./gradlew check
+  - ./gradlew test
+
+branches:
+  only:
+  - master
+
+before_cache:
+  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
+
+cache:
+  directories:
+    - $HOME/.gradle/caches/
+    - $HOME/.gradle/wrapper/