Fixes PSR2 errors for php-cs-fixer

Fixes [Travis errors](https://travis-ci.org/RWOverdijk/AssetManager/jobs/14932653#L182):

```
$ output=$(php php-cs-fixer.phar fix -v --dry-run --level=psr2 .); if [[ $output ]]; then while read -r line; do echo -e "\e[00;31m$line\e[00m"; done <<< "$output"; false; fi;
1) tests/AssetManagerTest/Service/AssetManagerTest.php (function_declaration)
2) tests/AssetManagerTest/Resolver/CollectionResolverTest.php (function_declaration)
3) src/AssetManager/Service/AssetCachanager.php (function_declaration)
4) src/AssetManager/Cache/FilePathCache.php (function_declaration)
```