Move script for checkout fixing to before_install

This should happen first before performing any other build steps to
ensure that the correct version information is always available.

Author: cboehme

.travis.yml

@@ -4,7 +4,7 @@ language: java
 jdk:
   - oraclejdk8
 
-install:
+before_install:
   - ./travis/switch-to-branch.sh
 
 after_success: