[CS2] Interpolated strings containing backticks are not properly escaped.

If a backtick is found inside an interpolated string, it doesn't get escaped, causing syntax errors.

Input:
```coffeescript
console.log("This is a test: `#{process.pid}`")
```
Result:
```javascript
console.log(`This is a test: `${process.pid}``);
```
Expected result:
```javascript
console.log(`This is a test: \`${process.pid}\``);
```