improve retrieval of Git checkouts for TravisCI.
improve retrieval of Git checkouts for TravisCI.

A delayed build process in Travis-CI might crash if there was an intermediate commit to the repository.
Lets fetch a few more commits.

sosy-lab/java-smt,sosy-lab/java-smt,sosy-lab/java-smt,sosy-lab/java-smt,sosy-lab/java-smt