Update "ci" npm script to run "build-demo" fully in parallel.

package.json

@@ -40,7 +40,7 @@
     "build-demo": "node scripts/index.mjs copy node_modules/markdown-it/dist/markdown-it.min.js demo/markdown-it.min.js && cd demo && webpack --no-stats",
     "build-docs": "node doc-build/build-rules.mjs",
     "build-example": "npm install --no-save --ignore-scripts grunt grunt-cli gulp through2",
-    "ci": "npm-run-all --continue-on-error --parallel lint serial-config-docs serial-declaration-demo test-cover && git diff --exit-code",
+    "ci": "npm-run-all --continue-on-error --parallel build-demo lint serial-config-docs serial-declaration test-cover && git diff --exit-code",
     "clone-test-repos-apache-airflow": "cd test-repos && git clone https://github.com/apache/airflow apache-airflow --depth 1 --no-tags --quiet",
     "clone-test-repos-dotnet-docs": "cd test-repos && git clone https://github.com/dotnet/docs dotnet-docs --depth 1 --no-tags --quiet",
     "clone-test-repos-electron-electron": "cd test-repos && git clone https://github.com/electron/electron electron-electron --depth 1 --no-tags --quiet && cd electron-electron && npm install --ignore-scripts @electron/lint-roller typescript@4",
@@ -58,7 +58,7 @@
     "lint": "eslint --max-warnings 0",
     "lint-test-repos": "ava --timeout=10m test/markdownlint-test-repos-*.mjs",
     "serial-config-docs": "npm run build-config && npm run build-docs",
-    "serial-declaration-demo": "npm run build-declaration && npm-run-all --continue-on-error --parallel build-demo test-declaration",
+    "serial-declaration": "npm run build-declaration && npm run test-declaration",
     "test": "ava --timeout=30s test/markdownlint-test.mjs test/markdownlint-test-config.mjs test/markdownlint-test-custom-rules.mjs test/markdownlint-test-fixes.mjs test/markdownlint-test-helpers.mjs test/markdownlint-test-micromark.mjs test/markdownlint-test-result-object.mjs test/markdownlint-test-scenarios.mjs helpers/test.cjs",
     "test-cover": "c8 --100 npm test",
     "test-declaration": "cd example/typescript && tsc --module commonjs && tsc --module nodenext && node type-check.js",