Add go 1.5 to test matrix
Add go 1.5 to test matrix

stellar/horizon,lackac/horizon,irisli/horizon,nullstyle/go-horizon,masonforest/horizon,masonforest/go-horizon,masonforest/horizon,masonforest/horizon,nullstyle/go-horizon,lackac/horizon,nullstyle/go-horizon,FredericHeem/go-horizon,FredericHeem/go-horizon,irisli/horizon,irisli/horizon,masonforest/go-horizon,masonforest/go-horizon,stellar/horizon,lackac/horizon,FredericHeem/go-horizon,stellar/horizon