【flowtype/React/Class】これ。how to fix 「Covariant property `[fn]` incompatible with contravariant use in ``` assignment of property `[fn]`」

flowtype.js

////error
this._increment = this._increment.bind(this);
                  ^^^^^^^^^^ property `_increment`. Covariant property `_increment` incompatible with contravariant use in
 27:         this._increment = this._increment.bind(this);
             ^^^^^^^^^^^^^^^ assignment of property `_increment`

/////// code ////////
    constructor(props: Props){
        super(props);
        this.state = {
            value : this.props.value
        }
        this._increment = this._increment.bind(this);////flowtype Error
        this._decrement = this._decrement.bind(this);////flowtype Error
    };
    _increment (e:any) {
        this.setState({
            value: this.state.value + 1
        })
    }
    _decrement (e:any) {
        this.setState({
            value: this.state.value -1
        })
    }
    
/////////