ruby: bump to 2.5.1

ruby: bump to 2.5.1

This release includes some bug fixes and some security fixes.

* CVE-2017-17742: HTTP response splitting in WEBrick
* CVE-2018-6914: Unintentional file and directory creation with directory traversal in tempfile and tmpdir
* CVE-2018-8777: DoS by large request in WEBrick
* CVE-2018-8778: Buffer under-read in String#unpack
* CVE-2018-8779: Unintentional socket creation by poisoned NUL byte in UNIXServer and UNIXSocket
* CVE-2018-8780: Unintentional directory traversal by poisoned NUL byte in Dir
* Multiple vulnerabilities in RubyGems

There are also some bug fixes.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>