[WebProfilerBundle] made token shorter in WDT

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

The length of the profiler token was increased by [this](https://github.com/symfony/symfony/commit/b9cdb9a26d2cf3ebad415b993784450aeee77ae6
) commit. This PR makes the visible token shorter.

Before:
![before](https://f.cloud.github.com/assets/162986/376901/338b9684-a461-11e2-9806-fc77d5ce5039.png)
After:
![after](https://f.cloud.github.com/assets/162986/376902/338ee078-a461-11e2-88c8-78748739565c.png)