docs: require npm v7

See https://github.blog/2021-02-02-npm-7-is-now-generally-available/

Author: coderbyheart

.github/workflows/semantic-release.yaml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2
         with:
-          node-version: "14.x"
+          node-version: "15.x"
       - name: Authenticate with NPM registry
         run: echo "//registry.npmjs.org/:_authToken=$NPM_TOKEN" >> ~/.npmrc
       - name: Keep npm cache around to speed up installs