docs: fix v2016.2.7 release notes

docs/releases/v2016.2.7.rst

 Gluon 2016.2.7
 ==============
 
-This release only fixes a single regression introduced in Gluon v2016.1.6.
+This release only fixes a single regression introduced in Gluon v2016.2.6, and
+add support for building using Perl 5.26.
 
 Bugfixes
 ~~~~~~~~
@@ -12,6 +13,8 @@ Bugfixes
   a node could hang forever in sysupgrade, requiring a power cycle. This has been
   fixed, triggering a reboot instead.
 
+* Backport fixes to support building with Perl 5.26 or newer (`76753ed <https://github.com/freifunk-gluon/gluon/commit/76753ede0da78e24208f10675fa288247deec961>`_)
+
 Known Issues
 ~~~~~~~~~~~~