Add invalidToken error

lib/errors.js

@@ -3,6 +3,7 @@ let Errors = {
 	accountAlreadyCreated: 'This account has already been created',
 	invalidLoginCredentials: 'Invalid login credentials were provided',
 	requestNotAuthorized: 'The request was not authorized',
+	invalidToken: 'The token provided was not valid',
 	missingParameter (param) {
 		return `The request is missing the parameter "${param}"`
 	},