Add vendor

Specifically because I want to modify a dependency

vendor/github.com/mattn/go-runewidth/runewidth_appengine.go

@@ -0,0 +1,9 @@
+//go:build appengine
+// +build appengine
+
+package runewidth
+
+// IsEastAsian return true if the current locale is CJK
+func IsEastAsian() bool {
+	return false
+}