bump patch version to 1.3.7

[kleinschmidt]

No breaking changes as far as I can tell since 1.3.6.

[codecov-io]

Codecov Report

Merging #360 into master will decrease coverage by 1.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #360      +/-   ##
==========================================
- Coverage   81.23%   80.14%   -1.09%     
==========================================
  Files           7        7              
  Lines         634      680      +46     
==========================================
+ Hits          515      545      +30     
- Misses        119      135      +16

Impacted Files	Coverage Δ
src/negbinfit.jl	81.69% <0%> (-11.3%)	⬇️
src/glmfit.jl	77.68% <0%> (-4.22%)	⬇️
src/lm.jl	94.25% <0%> (-0.87%)	⬇️
src/ftest.jl	98.46% <0%> (+0.02%)	⬆️
src/linpred.jl	64.58% <0%> (+1.42%)	⬆️
src/glmtools.jl	76.27% <0%> (+6.97%)	⬆️

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