www/otrs: Update to 5.0.26, Fixes multiple security vulnerabilities

Changes: https://www.otrs.com/release-notes-otrs-5s-patch-level-24/

		https://www.otrs.com/release-notes-otrs-5s-patch-level-25/
		https://www.otrs.com/release-notes-otrs-5s-patch-level-26/

PR: 224729
Submitted by: Vidar Karlsen <vidar@karlsen.tech>
Approved by: Mikhail Tsatsenko <m.tsatsenko@gmail.com> (maintainer)
MFH: 2017Q4
Security: cebd05d6-ed7b-11e7-95f2-005056925db4