double parentheses on template strings

I am getting a double parentheses when using template strings.

The following is just a dummy example...

```javascript
function logInvalid(obj) {
console.log(`${obj} is not valid.`);
}
```
gets compile to...
```javascript
function logInvalid(obj) {
console.log((obj + " is not valid."));
}
```
I am not sure that's the intended behavior.

see the life example [here](https://buble.surge.sh/#function%20logInvalid(obj)%20%7B%0A%20%20console.log(%60%24%7Bobj%7D%20is%20not%20valid.%60)%3B%0A%7D)