fix(smtp): remove extra semi in mime header

[piksel]

The MIME-Version header sent by the smtp service contained a trailing ; which seems to sometimes cause SpamAssassin to trigger the BOGUS_MIME_VERSION rule. Upon testing, this happened roughly 1/5 of the time, using the exact same message.

When removing the trailing ;, I have not been able to trigger the rule.

fixes #200

[codecov]

Codecov Report

Merging #201 (6dd5bdd) into main (441d5cf) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #201   +/-   ##
=======================================
  Coverage   76.87%   76.87%           
=======================================
  Files          85       85           
  Lines        2703     2703           
=======================================
  Hits         2078     2078           
  Misses        442      442           
  Partials      183      183           

Impacted Files	Coverage Δ
pkg/services/smtp/smtp.go	82.01% <100.00%> (ø)

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