fix: Restrict :has and :not to selector arguments

(fixes tree-sitter#45)

grammar.js

@@ -176,8 +176,19 @@ module.exports = grammar({
     pseudo_class_selector: $ => seq(
       optional($._selector),
       alias($._pseudo_class_selector_colon, ':'),
-      alias($.identifier, $.class_name),
-      optional(alias($.pseudo_class_arguments, $.arguments)),
+      choice(
+        // Either a `:has` or `:not` (which take only selectors)…
+        seq(
+          alias(choice('has', 'not'), $.class_name),
+          alias($.pseudo_class_has_or_not_arguments, $.arguments),
+        ),
+        // …or another pseudo-class (which can take a more diverse set of
+        // arguments).
+        seq(
+          alias($.identifier, $.class_name),
+          optional(alias($.pseudo_class_arguments, $.arguments)),
+        ),
+      ),
     ),
 
     pseudo_element_selector: $ => seq(
@@ -220,6 +231,12 @@ module.exports = grammar({
       ')',
     ),
 
+    pseudo_class_has_or_not_arguments: $ => seq(
+      token.immediate('('),
+      sep(',', $._selector),
+      ')',
+    ),
+
     pseudo_element_arguments: $ => seq(
       token.immediate('('),
       sep(',', choice($._selector, repeat1($._value))),