Bump eslint-config-react-app, fixes #142

[thms-rmb]

This is an attempt to fix the problem described in #142. Summary:

• There seems to be a problem with the dependency resolution during npm install.
• It seems the culprit is eslint-config-react-app@"^5.2.1", which transitively depends on eslint@"^5.0.0 || ^6.0.0", while eslint@"^7.7.0" was already specified as a dependency already.
• Bumping to eslint-config-react-app@"^6.0.0" seems to fix the problem.

[kpsherva]

thank you for your contribution!
the dependency which you are trying to upgrade will be centrally managed in another module and removed from this repository, therefore the fix will probably not be working in the future. Please check for alternative solution in #142 (comment)

[kpsherva]

thank you for your contribution!
the dependency which you are trying to upgrade will be centrally managed in another module and removed from this repository, therefore the fix will probably not be working in the future. Please check for alternative solution in #142 (comment)