page.waitForFunction fails because of whitespace

### Steps to reproduce
```
await page.waitForFunction(`
  (() => true)()`);
```
never returns, but

```
await page.waitForFunction(`(() => true)()`);
```
does. I expect them both to return immediately.

**Tell us about your environment:**

* Puppeteer version: 1.11.0
* Platform / OS version: MacOS
* URLs (if applicable):
* Node.js version: 8.9.1
