Bump version numbers to reflect 0.5.1 release

[Jauntbox]

No description provided.

[codecov]

Codecov Report

Merging #224 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #224      +/-   ##
==========================================
+ Coverage   86.33%   86.36%   +0.02%     
==========================================
  Files         310      310              
  Lines       10137    10137              
  Branches      347      347              
==========================================
+ Hits         8752     8755       +3     
+ Misses       1385     1382       -3

Impacted Files	Coverage Δ
.../op/features/types/FeatureTypeSparkConverter.scala	98.19% <0%> (+0.9%)	⬆️
...es/src/main/scala/com/salesforce/op/OpParams.scala	89.79% <0%> (+4.08%)	⬆️

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[salesforce-cla]

Thanks for the contribution! It looks like @Jauntbox is an internal user so signing the CLA is not required. However, we need to confirm this.