Revert "update Java to version 12 in TravisCI."
Revert "update Java to version 12 in TravisCI."

This reverts commit 071d5d47e189cdbee04a23e025b2d52519d4a635.

The new Java version does not solve the problem.
As before, the bug appears in TravisCI.

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