Update liquid docs for named parameters

The YARD liquid gem now supports specifying named parameters. For the
core liquid tags and filters this is the only object I could find that
needed to be updated.

lib/liquid/standardfilters.rb

@@ -877,7 +877,7 @@ def at_most(input, n)
     #   - [`nil`](/docs/api/liquid/basics#nil)
     # @liquid_syntax variable | default: variable
     # @liquid_return [untyped]
-    # @liquid_optional_param allow_false [boolean] Whether to use false values instead of the default.
+    # @liquid_optional_param allow_false: [boolean] Whether to use false values instead of the default.
     def default(input, default_value = '', options = {})
       options = {} unless options.is_a?(Hash)
       false_check = options['allow_false'] ? input.nil? : !Liquid::Utils.to_liquid_value(input)