Add TravisCI file for pull requests (#50)

* Add TravisCI file for pull requests

* Fix env var config

* Oracle JDK not available in the default travis env

* Add license header

* Do not use Maven toolchains

* Less verbose build

* Further reduce output

.travis.yml

@@ -0,0 +1,32 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+language: java
+
+env:
+  - LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8
+
+jdk:
+  - openjdk8
+
+sudo: false
+install: skip
+
+cache:
+  directories:
+    - $HOME/.m2
+
+script: mvn clean verify checkstyle:checkstyle -B -q -Dmaven.javadoc.skip=true -Dorg.slf4j.simpleLogger.defaultLogLevel=ERROR 
+