Migrate to universal-hash v0.5

[newpavlov]

Depends on RustCrypto/traits#965

[tarcieri]

Closing in favor of #155

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 31.33%. Comparing base (890e5ab) to head (1abe387).
⚠️ Report is 150 commits behind head on master.

Files with missing lines	Patch %	Lines
polyval/src/lib.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #148       +/-   ##
===========================================
- Coverage   54.94%   31.33%   -23.62%     
===========================================
  Files          14       15        +1     
  Lines         990      750      -240     
===========================================
- Hits          544      235      -309     
- Misses        446      515       +69     

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