switch travis env to trusty tahir (14.04)
switch travis env to trusty tahir (14.04)

[skip appveyor]

lengtche/beets,sampsyo/beets,shamangeorge/beets,beetbox/beets,pkess/beets,Kraymer/beets,ibmibmibm/beets,sampsyo/beets,shamangeorge/beets,mosesfistos1/beetbox,lengtche/beets,lengtche/beets,madmouser1/beets,jcoady9/beets,madmouser1/beets,xsteadfastx/beets,pkess/beets,lengtche/beets,MyTunesFreeMusic/privacy-policy,beetbox/beets,ibmibmibm/beets,mosesfistos1/beetbox,artemutin/beets,SusannaMaria/beets,pkess/beets,jcoady9/beets,diego-plan9/beets,artemutin/beets,MyTunesFreeMusic/privacy-policy,jackwilsdon/beets,jcoady9/beets,jackwilsdon/beets,jackwilsdon/beets,diego-plan9/beets,SusannaMaria/beets,madmouser1/beets,diego-plan9/beets,diego-plan9/beets,beetbox/beets,shamangeorge/beets,xsteadfastx/beets,madmouser1/beets,ibmibmibm/beets,xsteadfastx/beets,xsteadfastx/beets,MyTunesFreeMusic/privacy-policy,mosesfistos1/beetbox,artemutin/beets,sampsyo/beets,SusannaMaria/beets,Kraymer/beets,ibmibmibm/beets,artemutin/beets,Kraymer/beets,shamangeorge/beets,pkess/beets,sampsyo/beets,mosesfistos1/beetbox,beetbox/beets,MyTunesFreeMusic/privacy-policy,SusannaMaria/beets,jcoady9/beets,Kraymer/beets,jackwilsdon/beets