Update to yarn v2

Fixes #705

Author: pjonsson

.gitattributes

@@ -1 +1,3 @@
 CHANGES.md merge=union
+/.yarn/releases/** binary
+/.yarn/plugins/** binary

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
         uses: actions/setup-node@v1
         with:
           node-version: ${{ matrix.node-version }}
-      - run: rm -rf node_modules && yarn install --frozen-lockfile
+      - run: rm -rf node_modules && yarn install --immutable
       - run: yarn gulp lint release
         env:
           NODE_OPTIONS: "--max_old_space_size=4096"

.gitignore

@@ -29,3 +29,11 @@ yarn-error.log
 
 package-lock.json
 .nvmrc
+# https://v3.yarnpkg.com/getting-started/qa#which-files-should-be-gitignored
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions