Fix error if USER username/group contains capital

corpus/user.txt

@@ -3,10 +3,16 @@ No group
 ==================
 
 USER foo
+USER FooBar
+USER Foo-Bar
 
 ---
 
 (source_file
+	(user_instruction
+		user: (unquoted_string))
+	(user_instruction
+		user: (unquoted_string))
 	(user_instruction
 		user: (unquoted_string)))
 
@@ -15,10 +21,18 @@ With group
 ==================
 
 USER foo:bar
+USER foo:Bar
+USER foo:Bar-Bar
 
 ---
 
 (source_file
+	(user_instruction
+		user: (unquoted_string)
+		group: (unquoted_string))
+	(user_instruction
+		user: (unquoted_string)
+		group: (unquoted_string))
 	(user_instruction
 		user: (unquoted_string)
 		group: (unquoted_string)))

grammar.js

@@ -120,7 +120,7 @@ module.exports = grammar({
 
     _user_name_or_group: ($) =>
       seq(
-        choice(/([a-z][-a-z0-9_]*|[0-9]+)/, $.expansion),
+        choice(/([a-zA-Z][-A-Za-z0-9_]*|[0-9]+)/, $.expansion),
         repeat($._immediate_user_name_or_group_fragment)
       ),
 
@@ -130,7 +130,7 @@ module.exports = grammar({
 
     _immediate_user_name_or_group_fragment: ($) =>
       choice(
-        token.immediate(/([a-z][-a-z0-9_]*|[0-9]+)/),
+        token.immediate(/([a-zA-Z][-a-zA-Z0-9_]*|[0-9]+)/),
         $._immediate_expansion
       ),
 

src/grammar.json

@@ -558,7 +558,7 @@
           "members": [
             {
               "type": "PATTERN",
-              "value": "([a-z][-a-z0-9_]*|[0-9]+)"
+              "value": "([a-zA-Z][-A-Za-z0-9_]*|[0-9]+)"
             },
             {
               "type": "SYMBOL",
@@ -589,7 +589,7 @@
           "type": "IMMEDIATE_TOKEN",
           "content": {
             "type": "PATTERN",
-            "value": "([a-z][-a-z0-9_]*|[0-9]+)"
+            "value": "([a-zA-Z][-a-zA-Z0-9_]*|[0-9]+)"
           }
         },
         {