travis: add 'go fmt' test
travis: add 'go fmt' test

executed with only go 1.5.

Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

j-kato/gobgp,a16/gobgp,a16/gobgp,fujita/gobgp,osrg/gobgp,Dipsingh/gobgp,fujita/gobgp,j-kato/gobgp,tamihiro/gobgp,fujita/gobgp,ishidawataru/gobgp,a16/gobgp,osrg/gobgp,Dipsingh/gobgp,ishidawataru/gobgp,tamihiro/gobgp,a16/gobgp,osrg/gobgp,ramrunner/gobgp,osrg/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,fujita/gobgp,ishidawataru/gobgp,ramrunner/gobgp,tamihiro/gobgp,Dipsingh/gobgp,ramrunner/gobgp,j-kato/gobgp,tamihiro/gobgp