vendor: update dependencies with github.com/kardianos/govendor

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

@@ -0,0 +1,9 @@
+// +build !windows appengine
+
+package isatty
+
+// 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
+}