Removing ➥ from sf_cache_key lines

In the original symfony book, code was manually wrapped when it was too long, and ➥ inserted to denote wrapping.

On http://symfony.com/legacy/doc/gentle-introduction/1_4/en/12-Caching the manual wrapping is ignored, and a space inserted: 
![Chapter 12 - Caching 1_4 - Symfony](https://f.cloud.github.com/assets/89852/248492/d2b77c6e-8b11-11e2-844f-f574988b5154.png)

Copying the code results in no cache clearing - which is how I discovered this error.

I'd like to prevent other developers who obey the manual having to debug this too - would you include these fixes?