Parse digits in sigil modifiers (#3)

grammar.js

@@ -344,7 +344,7 @@ module.exports = grammar({
             )
           )
         ),
-        optional(alias(token.immediate(/[a-zA-Z]+/), $.sigil_modifiers))
+        optional(alias(token.immediate(/[a-zA-Z0-9]+/), $.sigil_modifiers))
       ),
 
     keywords: ($) =>

test/corpus/expression/sigil.txt

@@ -219,10 +219,20 @@ modifiers
 
 ~r/left|right/i
 ~r/left|right/iUx
+~r/left|right/0
+~r/left|right/u8
 
 ---
 
 (source
+  (sigil
+    (sigil_name)
+    (quoted_content)
+    (sigil_modifiers))
+  (sigil
+    (sigil_name)
+    (quoted_content)
+    (sigil_modifiers))
   (sigil
     (sigil_name)
     (quoted_content)