Fixed usage of Generator\DocBlock\Tag\ParamTag in ApiController

The current api generator is throwing a php warning from the usage of `DocBlock/Tag/ParamTag` class in `ApiController`.

    PHP Warning:  ltrim() expects parameter 1 to be string, array given in 
    ../vendor/zendframework/zendframework/library/Zend/Code/Generator/DocBlock/Tag/ParamTag.php on line 62

ZF2 class reference: https://github.com/zendframework/zf2/blob/master/library/Zend/Code/Generator/DocBlock/Tag/ParamTag.php#L27