Remove typehint string in `frameToBeAvailableAndSwitchToIt`

Type hints can not be used with scalar types such as int or string.

[See PHP documentation](http://www.php.net/manual/en/language.oop5.typehinting.php)
Merge pull request #119 from DaphDaOne/patch-1

Remove typehint string in `frameToBeAvailableAndSwitchToIt`