Try to fix the indentation.

grammar.js

@@ -3,27 +3,27 @@ module.exports = grammar({
 
   extras: $ => [
     $.comment,
-	$._line_break,
-	/[ \t\r]/
+    $._line_break,
+    /[ \t\r]/
   ],
 
   rules: {
     program: $ => repeat(seq($._statement, optional($._terminator))),
 
-	_statement: $ => choice($._expression),
-	_expression: $ => choice($._argument),
+  	_statement: $ => choice($._expression),
+  	_expression: $ => choice($._argument),
 
-	_argument: $ => choice($._primary),
+  	_argument: $ => choice($._primary),
 
-	_primary: $ => choice($._variable),
+  	_primary: $ => choice($._variable),
 
-	_variable: $ => choice($.identifier , 'nil', 'self'),
+  	_variable: $ => choice($.identifier , 'nil', 'self'),
 
-	identifier: $ => seq(repeat(choice('@', '$')), /[a-zA-Z_][a-zA-Z0-9_]*/),
+  	identifier: $ => seq(repeat(choice('@', '$')), /[a-zA-Z_][a-zA-Z0-9_]*/),
 
-	comment: $ => token(seq('#', /.*/)),
+  	comment: $ => token(seq('#', /.*/)),
 
-  _line_break: $ => '\n',
-	_terminator: $ => choice($._line_break, ';'),
+    _line_break: $ => '\n',
+  	_terminator: $ => choice($._line_break, ';'),
   }
 });