src/Mutator/Arithmetic/MinusEqual.php
public function mutate(Node $node)
    {
        return new Node\Expr\AssignOp\Plus($node->var, $node->expr, $node->getAttributes());
    }
public function mutate(Node $node)
    {
        return new Node\Expr\AssignOp\Plus($node->var, $node->expr, $node->getAttributes());
    }
public function mutate ( Node $ node ) { return new Node \ Expr \ AssignOp \ Plus ( $ node -> var , $ node -> expr , $ node -> getAttributes ( ) ) ; }
Replaces "-=" with "+="


@return Node\Expr\AssignOp\Plus
Replaces - = with + =