Merge pull request #1795 from joshtriplett/simplify-generic-params

Simplify GenericParams grammar

Author: traviscross

src/items/generics.md

@@ -3,9 +3,7 @@ r[items.generics]
 
 r[items.generics.syntax]
 ```grammar,items
-GenericParams ->
-      `<` `>`
-    | `<` (GenericParam `,`)* GenericParam `,`? `>`
+GenericParams -> `<` ( GenericParam (`,` GenericParam)* `,`? )? `>`
 
 GenericParam -> OuterAttribute* ( LifetimeParam | TypeParam | ConstParam )