ZOOKEEPER-3234: Add Travis-CI configuration file

Use Travis-CI in order to build ZooKeeper on multiple JDKs and run spotbugs on every supported JDK

Author: Enrico Olivelli <eolivelli@apache.org>

Reviewers: andor@apache.org

Closes #829 from eolivelli/fix/travis-35

(cherry picked from commit cde09d8eb608645353582978d5c03c11e99c753e)
Signed-off-by: Andor Molnar <andor@apache.org>

.travis.yml

@@ -0,0 +1,17 @@
+language: java
+sudo: false
+jdk:
+  - openjdk8
+  - openjdk11
+
+cache:
+  directories:
+  - "$HOME/.m2"
+
+script: mvn clean install -DskipTests spotbugs:check
+
+branches:
+  only:
+  - master
+  - branch-3.5
+  - branch-3.4