clean up code

- travisci is long dead
- golangci-lint the repo

hotp_test.go

@@ -7,10 +7,6 @@ import (
 
 var testKey = []byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
 
-func newZeroHOTP() *HOTP {
-	return NewHOTP(testKey, 0, 6)
-}
-
 var rfcHotpKey = []byte("12345678901234567890")
 var rfcHotpExpected = []string{
 	"755224",