Linter fails with two 'no-duplicate-imports' errors

[jreyesr]

(This issue was first reported by @falconhome in #97 (comment))

When running npx yarn dev after having run npx run upgrade, the linter fails with two violations of the no-duplicate-imports rule in ESLint. This makes it impossible to build the plugin.

Steps to reproduce

1. Clone grafana-map-panel with git clone https://github.com/panodata/grafana-map-panel
2. Run npx yarn install
3. Run npx yarn dev. It should run without issue (at least it does on my machine). If it fails, skip to step 5.
4. If the previous step didn't fail, run npx yarn upgrade.
5. Run npx yarn dev again. It should fail with two 'leaflet' import is duplicated no-duplicate-imports errors, on files src/worldmap.ts and src/types/leaflet_plus.d.ts

Cause

When cloning and running npx yarn install, version 7.3.1 of package @grafana/toolkit is downloaded. This package requires version 2.0.3 of @grafana/eslint-config. These two versions come from the yarn.lock file.

After running npx yarn upgrade, @grafana/toolkit is (in my tests) upgraded to version 7.5.7, which specifies version 2.3.0 of @grafana/eslint-config. However, the no-duplicate-imports rule was added on version 2.2.0 of @grafana/eslint-config.