add vendor data

vendor/github.com/dunglas/httpsfv/utils.go

@@ -0,0 +1,16 @@
+package httpsfv
+
+// isLowerCaseAlpha checks if c is a lower cased alpha character.
+func isLowerCaseAlpha(c byte) bool {
+	return 'a' <= c && c <= 'z'
+}
+
+// isAlpha checks if c is an alpha character.
+func isAlpha(c byte) bool {
+	return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z')
+}
+
+// isDigit checks if c is a digit.
+func isDigit(c byte) bool {
+	return '0' <= c && c <= '9'
+}