Improvement: Utilize @babel/plugin-proposal-class-properties by using…

[tomegz]

… class properties in class components

[coveralls]

Coverage decreased (-0.4%) to 93.586% when pulling f5ac576 on tomegz:improvement/class-properties into 50992a8 on patw0929:master.

[tomegz]

There is no need for using .bind with this plugin, we can use class properties. Ex.:

class MyClass extends React.Component {
  constructor() {
    super()
    this.someMethod = this.someMethod.bind(this)
  }

  someMethod() {
    // ...
  }
}

can be simply replaced by:

class MyClass extends React.Component { 
  someMethod = () => {
    // ...
  }
}