Replace == with ≈ in README for consistency

[torfjelde]

Replaces == with ≈ as suggested in #129 .

[codecov]

Codecov Report

Merging #131 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #131      +/-   ##
==========================================
+ Coverage   54.27%   54.31%   +0.03%     
==========================================
  Files          23       23              
  Lines        1402     1401       -1     
==========================================
  Hits          761      761              
+ Misses        641      640       -1     

Impacted Files	Coverage Δ
src/transformed_distribution.jl	54.28% <0.00%> (+0.51%)	⬆️

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