Constant folding inlines array instead of concatenating it

[merih]

babel-plugin-minify-constant-folding plugin converts

function (x) {
    return [].concat(x);
}

into

function (x) {
    return [x];
}

which poses a problem when x is an array.

Probably introduced in #505

[edc]

Same here. This breaks react-router and possibly other React packages because of how class is transpiled with babel: _this = _possibleConstructorReturn(this, _React$Component.call.apply(_React$Component, [this].concat(args))). That concat always fails with this bug, because it is converted to [this, args].

[boopathi]

Fixed in #578