move back to just python 2.7 in travis
move back to just python 2.7 in travis

ARMmbed/yotta,BlackstoneEngineering/yotta,stevenewey/yotta,bridadan/yotta,theotherjimmy/yotta,BlackstoneEngineering/yotta,iriark01/yotta,autopulated/yotta,ntoll/yotta,autopulated/yotta,theotherjimmy/yotta,eyeye/yotta,iriark01/yotta,bridadan/yotta,eyeye/yotta,ARMmbed/yotta,stevenewey/yotta,ntoll/yotta