fix(deps): update dependency gatsby-plugin-material-ui to v2.1.9

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
gatsby-plugin-material-ui	dependencies	patch	2.1.8 -> 2.1.9

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Release Notes

hupe1980/gatsby-plugin-material-ui

### [`v2.1.9`](https://togithub.com/hupe1980/gatsby-plugin-material-ui/compare/v2.1.8...v2.1.9) [Compare Source](https://togithub.com/hupe1980/gatsby-plugin-material-ui/compare/v2.1.8...v2.1.9)

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Codecov Report

Merging #223 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #223   +/-   ##
=======================================
  Coverage   37.80%   37.80%           
=======================================
  Files          34       34           
  Lines         283      283           
  Branches       37       37           
=======================================
  Hits          107      107           
  Misses        155      155           
  Partials       21       21           

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