travis: use explicit go minor release versions
travis: use explicit go minor release versions

Turns out `1.x` no longer means `latest 1.x.y` (if it ever did).

endocode/fleet,dongsupark/fleet,jonboulle/fleet,dongsupark/fleet,coreos/fleet,dalbani/fleet,esatterwhite/fleet,improbable-io/fleet,giantswarm/fleet,dongsupark/fleet,dalbani/fleet,giantswarm/fleet,coreos/fleet,endocode/fleet,paveltiunov/fleet,paveltiunov/fleet,mookjp/fleet,endocode/fleet,jonboulle/fleet,esatterwhite/fleet,bviswana101/fleet,mookjp/fleet,coreos/fleet,bviswana101/fleet,improbable-io/fleet,jonboulle/fleet,dalbani/fleet,improbable-io/fleet,giantswarm/fleet