fix ocramius/proxy-manager dependency version

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

Symfony 2.5 and higher requires ocramius/proxy-manager 0.4.0 or
higher.