Apply fixes from StyleCI

[rennokki]

This pull request applies code style fixes from an analysis carried out by StyleCI.

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For more information, click here.

[codecov-io]

Codecov Report

Merging #1 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##             master    #1   +/-   ##
======================================
  Coverage        90%   90%           
  Complexity       12    12           
======================================
  Files             2     2           
  Lines            30    30           
======================================
  Hits             27    27           
  Misses            3     3

Impacted Files	Coverage Δ	Complexity Δ
src/LaravelMJML.php	89.28% <100%> (ø)	10 <0> (ø)	⬇️

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