Update to 2.28

Upstream changes:
Version 2.28 - 11th October 2018
#------------------------------------------------------------------------

* Add and enable Travis CI to track GitHub Pull Requests

* Template is now using GitHub as the official Bug Tracker

* Nicolas R. fixed a circular reference in Template::Plugin::Filter
  https://github.com/abw/Template2/issues/152

* Nicolas R. adjusted group regexes to not be greedy
  https://github.com/abw/Template2/issues/94

* Nicolas R. added unit tests to cover regression from RT 91172
  https://github.com/abw/Template2/issues/122

* Nicolas R. added support for template files having mtime=0
  https://github.com/abw/Template2/issues/102

* Todd Rinaldo fixed rand calls with no args in Math plugin
  https://github.com/abw/Template2/issues/155

* Todd Rinaldo corrected ttree 2.22 logic change
  https://github.com/abw/Template2/issues/148

* Todd Rinaldo turned off automated testing for tests using optional modules
  https://github.com/abw/Template2/issues/156

* Nicolas R. adjusted unit tests to not force Stash::XS

* Nicolas R. added a pre allocated buffer in Stash.xs to avoid malloc/free
  https://github.com/abw/Template2/issues/82

* Nicolas R. optmized Template::Parser by avoiding a dummy sub
  https://github.com/abw/Template2/issues/83

* Nicolas R. optimized Template:Directive by using index
  https://github.com/abw/Template2/issues/84

* Nicolas R. adjust _dotop logic in Stash for perl 5.28 and earlier
  https://github.com/abw/Template2/issues/81

* Todd Rinaldo documented VMethod method called 'item'
  https://github.com/abw/Template2/issues/90

* Nicolas R. adjusted t/filter.t after recent switch to RFC3986
  https://github.com/abw/Template2/issues/179

* Nicolas R. fixed warnings from t/cgi.t
  https://github.com/abw/Template2/issues/178

* Ivan Krylov added STRICT option to ttree
  https://github.com/abw/Template2/issues/81

* Kent Fredric fixed relative path handling in templates on Perl 5.26+
  https://github.com/abw/Template2/issues/80

* Tom Delmas fixed some typo from documentation
  https://github.com/abw/Template2/issues/76

* Matthew Somerville switched uri/url to use RFC3986
  updated the documentation to match the history.
  https://github.com/abw/Template2/issues/35

* Sebastien Deseille used remove_tree helper to remove directories
  https://github.com/abw/Template2/issues/67

* Nick Hibma - Add Sortkeys to DUMPER_ARGS
  https://github.com/abw/Template2/issues/64

* E. Choroba added a warn on duplicate block name
  https://github.com/abw/Template2/issues/61

* Jason Lewis fixed some typo in ttree.pod
  https://github.com/abw/Template2/issues/58


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