Pass null for _active property_ on initial call to the Expansion algorithm from expand().

Fixes #374.

Author: gkellogg

index.html

@@ -5768,8 +5768,9 @@ <h3>Algorithm</h3>
             passing the <var>active context</var>,
             {{RemoteDocument/document}} from <var>remote document</var> or <a data-lt="jsonldprocessor-expand-input">input</a>
             if there is no <var>remote document</var> as <var>element</var>,
+            `null` as <var>active property</var>,
             {{RemoteDocument/documentUrl}} as <var>base URL</var>, if available, otherwise to {{JsonLdOptions/base}},
-            and <span class="changed">{{JsonLdOptions/frameExpansion}}</span>
+            and the <span class="changed">{{JsonLdOptions/frameExpansion}}</span>
             and <span class="changed">and {{JsonLdOptions/ordered}}</span>
             flags from <a data-lt="jsonldprocessor-compact-options">options</a>.
             <ol id="api-expand-post-processing" class="changed">