add message for numeric string rule

Author: andersonjoseph

lib/messages.js

@@ -11,6 +11,7 @@ module.exports = {
 	stringPattern: "The '{field}' field fails to match the required pattern!",
 	stringContains: "The '{field}' field must contain the '{expected}' text!",
 	stringEnum: "The '{field}' field does not match any of the allowed values!",
+	stringNumeric: "The '{field}' field must be a numeric string",
 
 	number: "The '{field}' field must be a number!",
 	numberMin: "The '{field}' field must be greater than or equal to {expected}!",