Fix CVE-2018-12356 by hardening the regex.
Fix CVE-2018-12356 by hardening the regex.

fixes and closes #219


Former-commit-id: b4e9a2f9405a6b1f8ce45b502ffb90b2da111b8b
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin