Update README.md to be more colorblind friendly

[jatins]

Checklist before merging this PR:

• [ ] Mentioned all issues that this PR fixes or addresses.
• [ ] Summarized the updates of this PR under Summary.
• [ ] Added an entry under Unreleased in the Changelog.

Fixes #.

Summary

I had trouble differentiation green/red squares in readme, this make it a little more colorblind friendly. I just find/replaced the emojis so the rest of text should be unchanged

Other Information

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.78%. Comparing base (5c8b366) to head (20ccc43).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2433      +/-   ##
==========================================
- Coverage   93.79%   93.78%   -0.02%     
==========================================
  Files         138      138              
  Lines       14654    14640      -14     
==========================================
- Hits        13745    13730      -15     
- Misses        909      910       +1     

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[jatins]

@dennisbader thanks for having a look! Changes:

• Updated the changelog
• removed redundant whitespace