[SecurityBundle] remove short array syntax

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

The short array syntax was introduced in PHP 5.4 and therefore leads
to failing tests when executed in PHP 5.3 environments.