chore: migrate to yarn@2

.github/workflows/test.yml

@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [macos-10.14, ubuntu-18.04, windows-2019]
+        os: [ubuntu-latest]
 
     steps:
       - name: Check out Git repository
@@ -17,22 +17,10 @@ jobs:
       - name: Install Node.js, NPM and Yarn
         uses: actions/setup-node@v1
         with:
-          node-version: 14
-
-      - name: Get yarn cache directory path
-        id: yarn-cache-dir-path
-        run: echo "::set-output name=dir::$(yarn cache dir)"
-
-      - uses: actions/cache@v2
-        id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
-        with:
-          path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
-          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-yarn-
+          node-version: 15
 
       - name: yarn install
-        run: yarn --frozen-lockfile
+        run: yarn --immutable
 
       - name: yarn test
         env:

.gitignore

@@ -27,3 +27,6 @@ node_modules
 npm-debug.log.*
 .env
 dist
+
+.yarn/unplugged
+.yarn/build-state.yml