Remove silent hard dependency on PHPUnit. Fixes #820

[dvdoug]

No description provided.

[codecov]

Codecov Report

Merging #822 into master will decrease coverage by 0.00%.
The diff coverage is 34.61%.

@@             Coverage Diff              @@
##             master     #822      +/-   ##
============================================
- Coverage     83.36%   83.35%   -0.01%     
  Complexity     1104     1104              
============================================
  Files            62       62              
  Lines          3618     3622       +4     
============================================
+ Hits           3016     3019       +3     
- Misses          602      603       +1     

Impacted Files	Coverage Δ	Complexity Δ
src/Report/Html/Renderer/File.php	93.62% <17.64%> (+0.01%)	135.00 <0.00> (ø)
src/CodeCoverage.php	44.95% <66.66%> (+0.27%)	96.00 <0.00> (ø)

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