Fix: Bring back support for PHP 7.1

[localheinz]

This PR

• brings back support for PHP 7.1

Related to #266.

[codecov]

Codecov Report

Merging #280 into master will decrease coverage by 0.84%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #280      +/-   ##
============================================
- Coverage     87.03%   86.18%   -0.85%     
  Complexity       35       35              
============================================
  Files             2        2              
  Lines           162      181      +19     
============================================
+ Hits            141      156      +15     
- Misses           21       25       +4

Impacted Files	Coverage Δ	Complexity Δ
src/Command/NormalizeCommand.php	86.98% <0%> (-1.1%)	32% <0%> (ø)
src/NormalizePlugin.php	75% <0%> (+2.27%)	3% <0%> (ø)	⬇️

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