Use http4s-blaze-client for forking instead of curl

[fthomas]

No description provided.

[codecov]

Codecov Report

Merging #40 into master will increase coverage by 0.43%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
+ Coverage   25.33%   25.77%   +0.43%     
==========================================
  Files          12       12              
  Lines         296      291       -5     
  Branches        5        5              
==========================================
  Hits           75       75              
+ Misses        221      216       -5

Impacted Files	Coverage Δ
...t/scalasteward/gh/http4s/Http4sGitHubService.scala	0% <0%> (ø)
...c/main/scala/eu/timepit/scalasteward/steward.scala	0% <0%> (ø)	⬆️

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