Fix enumerable.rbs

Author: soutaro

core/enumerable.rbs

@@ -529,7 +529,7 @@ module Enumerable[unchecked out Elem] : _Each[Elem]
   def entries: () -> ::Array[Elem]
 
   def enum_for: (Symbol method, *untyped, **untyped) ?{ (?) -> Integer } -> Enumerator[untyped, untyped]
-    | () ?{ () -> Integer } -> Enumerator[Elem, self]
+              | () ?{ () -> Integer } -> Enumerator[Elem, self]
 
   %a{annotate:rdoc:skip}
   alias to_enum enum_for