use mvn install in script/build_for_travis.sh instead of using the Travis mvn default

Author: mikesamuel

.travis.yml

@@ -11,4 +11,5 @@ jdk:
 
 # Test each version with an appropriate Java version and flags to disable
 # GPG signing so that we don't have to provision Travis with private keys.
+install: true
 script: "$TRAVIS_BUILD_DIR/scripts/build_for_travis.sh"