Add missing "?" notion
> **<sup>Syntax</sup>**\
> _TypeAlias_ :\
> &nbsp;&nbsp; `type` [IDENTIFIER]&nbsp;[_GenericParams_]<sup>?</sup>
-> [_WhereClause_]<sup>?</sup> ( `=` [_Type_] ) `;`
+> [_WhereClause_]<sup>?</sup> ( `=` [_Type_] )<sup>?</sup> `;`
A _type alias_ defines a new name for an existing [type]. Type aliases are
declared with the keyword `type`. Every value has a single, specific type, but
