Update Go to 1.15 on Travis CI
Update Go to 1.15 on Travis CI

Signed-off-by: Krzysztof Wilczyński <5f1c0be89013f8fde969a8dcb2fa1d522e94ee00@linux.com>

kwilczynski/go-magic,kwilczynski/go-magic,kwilczynski/go-magic