Fix: Use localheinz/diff instead of sebastian/diff

[localheinz]

This PR

• uses localheinz/diff instead of sebastian/diff

Fixes #186.

[codecov]

Codecov Report

Merging #207 into 1.x will decrease coverage by 0.68%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                1.x     #207      +/-   ##
============================================
- Coverage     32.36%   31.68%   -0.69%     
+ Complexity       42       41       -1     
============================================
  Files             3        3              
  Lines           207      202       -5     
============================================
- Hits             67       64       -3     
+ Misses          140      138       -2

Impacted Files	Coverage Δ	Complexity Δ
src/Command/NormalizeCommand.php	35.75% <100%> (-0.66%)	34 <0> (-1)

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