Missing use of required Expansion input variable in expand()

[kasei]

(Related to #265, #356)

expand() step 7:

Set expanded output to the result of using the Expansion algorithm, passing the active context, document from remote document or input if there is no remote document as element, documentUrl as base URL, and frameExpansion and and ordered flags from options.

Expansion 5.1.2 says active property is a required input variable, but it is not supplied at this callsite.

[gkellogg]

Updated in #377.

[kasei]

@gkellogg #377 looks good. Thanks.