Fix flay to ~> 2.13.0

[faisal]

Bump Flay to 2.14, which switches to Prism for parsing.

Check list:

• Add an entry to the changelog
• Squash all commits into a single one
• Describe your PR, link issues, etc.

[faisal]

Looks like the true fix is in #551. Closing.

[faisal]

This will fail until #548 is addressed.

[faisal]

Correction: this will not actually work until we resolve the incompatibility with Flog 4.9:

Because flay >= 2.14.0 depends on path_expander ~> 2.0
  and flog >= 4.4.0, < 4.9.0 depends on path_expander ~> 1.0,
  flay >= 2.14.0 is incompatible with flog >= 4.4.0, < 4.9.0.
And because every version of rubycritic depends on flay ~> 2.14.0,
  flog >= 4.4.0, < 4.9.0 is incompatible with rubycritic >= 0.
So, because every version of rubycritic depends on flog ~> 4.8.0
  and Gemfile depends on rubycritic >= 0,
  version solving has failed.