fix typo

lib/liquid/tokenizer.rb

@@ -7,7 +7,7 @@ module Liquid
     attr_reader :line_number, :for_liquid_tag
 
     TAG_END = /%\}/
-    TAG_OR_VARIABLE_START = /\{[\{\%}]/
+    TAG_OR_VARIABLE_START = /\{[\{\%]/
     NEWLINE = /\n/
 
     OPEN_CURLEY = "{".ord

test/unit/tokenizer_unit_test.rb

@@ -6,6 +6,7 @@ class TokenizerTest < Minitest::Test
   def test_tokenize_strings
     assert_equal([' '], tokenize(' '))
     assert_equal(['hello world'], tokenize('hello world'))
+    assert_equal(['{}'], tokenize('{}'))
   end
 
   def test_tokenize_variables