Akismet for JS 0.8.0

• Breaking change: using more ES2015 features, like default parameters and destructuring assignment.
• Breaking change: raised the required Node.js version.
• Breaking change: fixed the signature and behavior of the toJSON() methods.
• Breaking change: changed the case of the Client.serviceUrl and Server.redirectUrl properties.
• Turned the package into a scoped one.
• Added the DEFAULT_HOST and DEFAULT_PORT constants to the Server class.
• Added more unit tests.
• Replaced SonarQube code analyzer by Codacy service.
• Improved the code coverage.