fix grammar

Author: tbrowder

doc/Type/Encoding/Registry.pod6

@@ -35,7 +35,7 @@ X<|Encoding::Decoder>
 
     method find(Str() $name)
 
-Finds an encoding by their name. Returns an C<Encoding::Encoder> or
+Finds an encoding by its name. Returns an C<Encoding::Encoder> or
 C<Encoding::Decoder>, depending on what had been registered.
 
 =end pod