travis: Fix caching issues

Author: MarcoFalke

.travis/test_06_script_b.sh

@@ -25,3 +25,5 @@ if [ "$RUN_FUZZ_TESTS" = "true" ]; then
   DOCKER_EXEC test/fuzz/test_runner.py -l DEBUG ${DIR_FUZZ_IN}
   END_FOLD
 fi
+
+cd ${TRAVIS_BUILD_DIR} || (echo "could not enter travis build dir $TRAVIS_BUILD_DIR"; exit 1)