Does not strip comments from interpolated expressions

Comments are not removed from code that uses interpolated expressions.

For example if campers have a line of code like :

```js
const v = /*a*/`/*b*/${/*c*/12}`;
```

The expected output should be

```js
const v = `/*b*/${12}`;
```

However we end up with the following

```js
const v = `/*b*/${/*c*/12}`;
```

Copied from: https://github.com/jonschlinkert/strip-comments/issues/54