Use `travis_wait`: avoid fail due to no output
Use `travis_wait`: avoid fail due to no output

Previous run on this file failed due to no output for 10min:
https://travis-ci.org/OpenTSDB/asyncbigtable/jobs/202984010

Travis recommends using `travis_wait` command in such cases:
https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received

Commands were taken from the Travis docs for Maven projects:
https://docs.travis-ci.com/user/languages/java/#Projects-Using-Maven

manolama/asyncbigtable,OpenTSDB/asyncbigtable