Revert "Merge pull request #463 from Shopify/stricter-identifiers"

This reverts commit a056f6521c, reversing
changes made to 7843bcca8d.

test/unit/lexer_unit_test.rb

@@ -31,8 +31,8 @@ class LexerUnitTest < Minitest::Test
   end
 
   def test_fancy_identifiers
-    tokens = Lexer.new('hi five?').tokenize
-    assert_equal [[:id,'hi'], [:id, 'five'], [:question, '?'], [:end_of_string]], tokens
+    tokens = Lexer.new('hi! five?').tokenize
+    assert_equal [[:id,'hi!'], [:id, 'five?'], [:end_of_string]], tokens
   end
 
   def test_whitespace