fix (build): use yarn for doc deps installation

Author: kepelrs

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
           node-version: '14'
       - run: cd test && npm i && cp .env-example .env && cd ..
       - run: npm install -g codecov
-      - run: cd docs && npm i && npm run build && cd ..
+      - run: cd docs && yarn install && npm run build && cd ..
       - run: npm i -g yarn
       - run: yarn install
       - run: npm run test:cov && codecov