Use location for #to_s

Some tokens doesn't have `location`. `#to_s` raises NoMethodError
for such cases if the method uses `line` and `column`.

lib/lrama/lexer/token.rb

@@ -5,7 +5,7 @@ class Token < Struct.new(:s_value, :alias_name, :location, keyword_init: true)
       attr_accessor :referred
 
       def to_s
-        "#{super} line: #{line}, column: #{column}"
+        "#{super} location: #{location}"
       end
 
       def referred_by?(string)