Purge unused dependencies.
Update dependencies to latest except:
- ts-lint. Keep locked to 9.0.1 because that's the latest version that
works with Webpack 4 that's still used by
vue-cli-plugin-electron-builder.
- Keep eslint at version 7 because tests cannot be run/compiled with
version 7, see eslint/eslint#15678, vuejs/vue-cli#6759.
Newer versions of ESLint modules do not allow linebreak after or before
= operator (operator-linebreak). This commit also changes files to
comply with it.
Closes#116, #119, #122, #130.
