bump golang version and use go.mod

2 jobs for master in 1 minute (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #7231
run go checks

00:01:00

failed #7228
run go checks

00:00:12

 
Name Stage Failure
failed
run go checks Test
	/usr/local/go/src/github.com/wcharczuk/go-chart/util (from $GOROOT)
/go/src/github.com/wcharczuk/go-chart/util (from $GOPATH)
build.go:25:3: cannot find package "golang.org/x/oauth2" in any of:
/usr/local/go/src/golang.org/x/oauth2 (from $GOROOT)
/go/src/golang.org/x/oauth2 (from $GOPATH)
global.go:23:3: cannot find package "golang.org/x/oauth2/github" in any of:
/usr/local/go/src/golang.org/x/oauth2/github (from $GOROOT)
/go/src/golang.org/x/oauth2/github (from $GOPATH)
ERROR: Job failed: exit code 1