Typo in grammar for ~P (#449)

Otherwise the grammar only allows `~P` on the final element of a list.

Author: amartini51

TSPL.docc/ReferenceManual/Types.md

@@ -1350,7 +1350,7 @@ to specify the type of its raw values, see <doc:Enumerations#Raw-Values>.
 > Grammar of a type inheritance clause:
 >
 > *type-inheritance-clause* → **`:`** *type-inheritance-list* \
-> *type-inheritance-list* → *attributes*_?_ **`~`**_?_ *type-identifier* | *attributes*_?_ *type-identifier* **`,`** *type-inheritance-list*
+> *type-inheritance-list* → *attributes*_?_ **`~`**_?_ *type-identifier* | *attributes*_?_ **`~`**_?_ *type-identifier* **`,`** *type-inheritance-list*
 
 ## Type Inference