README: add travis svg badge showing build status
README: add travis svg badge showing build status

aakselrod/lnd,LightningNetwork/lnd,AndrewSamokhvalov/lnd,LightningNetwork/lnd,ddustin/lnd,bryanvu/lnd,bryanvu/lnd,aakselrod/lnd,ddustin/lnd,AndrewSamokhvalov/lnd