Add dependabot config

[jtakalai]

For semi-automated dependency updates, yay!

In vein of #758, these little-used dependencies might stray out of date easily. Luckily, github offers dependency update spam service, if you're willing to consider/accept it ;)

[codecov-commenter]

Codecov Report

Base: 95.90% // Head: 95.90% // No change to project coverage 👍

Coverage data is based on head (1f7cca7) compared to base (8d49be0).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #759   +/-   ##
=======================================
  Coverage   95.90%   95.90%           
=======================================
  Files          19       19           
  Lines        1050     1050           
=======================================
  Hits         1007     1007           
  Misses         43       43           

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[cgewecke]

Thanks!