Adding openjdk6 and maven3.0 in travis.yml

Travis has removed openjdk6 for saving space, hence adding it from addon and the version of maven which is by default used in travis  requires minimum jdk7, hence installing specific version of maven.

For more info refer : 
https://docs.travis-ci.com/user/reference/trusty/#jvm-clojure-groovy-java-scala-images
travis-ci/travis-ci#8452

Author: raghuhit

.travis.yml

@@ -1,8 +1,23 @@
 language: java
 
+addons:
+  apt:
+    packages:
+      - openjdk-6-jdk
+      
 jdk:
+  - openjdk6
   - oraclejdk8
   - openjdk7
   - openjdk8
+ 
+ install:
+  - echo "Downloading Maven 3.0";
+  - wget https://archive.apache.org/dist/maven/binaries/apache-maven-3.0-bin.zip || travis_terminate 1
+  - unzip -qq apache-maven-3.0-bin.zip || travis_terminate 1
+  - export M2_HOME=$PWD/apache-maven-3.0
+  - export PATH=$M2_HOME/bin:$PATH
+  - mvn -version
+  - mvn clean package install -DskipTests -Dgpg.skip
 
 after_failure: cat /home/travis/build/browserstack/browserstack-local-java/target/surefire-reports/*