use go1.11 with go mod

vendor/github.com/mattn/go-isatty/isatty_appengine.go

@@ -1,15 +0,0 @@
-// +build appengine
-
-package isatty
-
-// IsTerminal returns true if the file descriptor is terminal which
-// is always false on on appengine classic which is a sandboxed PaaS.
-func IsTerminal(fd uintptr) bool {
-	return false
-}
-
-// IsCygwinTerminal() return true if the file descriptor is a cygwin or msys2
-// terminal. This is also always false on this environment.
-func IsCygwinTerminal(fd uintptr) bool {
-	return false
-}