Remove ESLint

Prettier is preferred. https://prettier.io/

Yorkie was only installed as a dependency of @vue/cli-plugin-eslint, so
it has been added as a dev dependency.

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Build application
         run: npm run build
       - name: Check formatting
-        run: npm run lint:all
+        run: npm run lint
       - name: Run unit tests
         run: npm run test:unit
         env:

README.md

@@ -1,5 +1,7 @@
 # vue-mastery-testing-app
 
+Vue CLI 4 app for [Vue Mastery unit testing course](https://www.vuemastery.com/courses/unit-testing/what-to-test)
+
 ## Project setup
 
 ```
@@ -28,8 +30,25 @@ npm run test:unit
 
 ```
 npm run lint
+npm run fix
 ```
 
 ### Customize configuration
 
 See [Configuration Reference](https://cli.vuejs.org/config/).
+
+Configuration settings used initially:
+
+```
+Vue CLI v4.3.0
+? Please pick a preset: Manually select features
+? Check the features needed for your project: Babel, Router, Vuex, Linter, Unit
+? Use history mode for router? (Requires proper server setup for index fallback in production) Yes
+? Pick a linter / formatter config: Prettier
+? Pick additional lint features: Lint on save, Lint and fix on commit
+? Pick a unit testing solution: Jest
+? Where do you prefer placing config for Babel, ESLint, etc.? In dedicated config files
+? Save this as a preset for future projects? (y/N) N
+```
+
+When [Prettier](https://prettier.io/) is selected, Vue CLI also includes ESLint, which is unnecessary. Some additional configuration is needed to remove ESLint.