Rely on a hermes fork to pass custom template functions

[jinroh]

This is mainly done in order to fix the go.uuid API breaking changes, since hermes rely on sprig which rely on this library.

We should introduce quickly the new go dep tool in order to lock our dependencies and avoid these kind of issues in the near future.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@506dd03). Click here to learn what that means.
The diff coverage is 100%.

@@           Coverage Diff            @@
##             master   #1148   +/-   ##
========================================
  Coverage          ?   84.9%           
========================================
  Files             ?     178           
  Lines             ?   52330           
  Branches          ?       0           
========================================
  Hits              ?   44429           
  Misses            ?    6470           
  Partials          ?    1431

Impacted Files	Coverage Δ
pkg/workers/mails/mail_templates.go	93.35% <100%> (ø)

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