message: build: Move to forked piwik plugin
  Fixes mixed content issues
diff: "devDependencies": {
  "gitbook": "^3.2.3",
  "gitbook-cli": "^2.3.2",
  - "gitbook-plugin-piwik": "^0.2.1",
  + "gitbook-plugin-piwik": "git+https://github.com/qdot/gitbook-plugin-piwik",
  "gitbook-plugin-mermaid-gb3": "git+https://github.com/galdo666/gitbook-plugin-mermaid-gb3.git#050021acf578d886e65cadb74505a7a43be3a031",
  "yarn": "^1.7.0"
  }
  