Fix minor compaction algorithm bug

Thanks to @dlongley for spotting it

This addresses #253.

Author: lanthaler

spec/latest/json-ld-api/index.html

@@ -1984,8 +1984,8 @@ <h3>Algorithm</h3>
                       a <tref>reverse property</tref>
                       <ol class="algorithm">
                         <li>If the <tref>term definition</tref> for <i>property</i> in
-                          the <tref>active context</tref> does not have a
-                          <tref>container mapping</tref> of <code>@set</code>,
+                          the <tref>active context</tref> has a
+                          <tref>container mapping</tref> of <code>@set</code> or
                           <code class="idlMemberName"><a href="#widl-JsonLdOptions-compactArrays">compactArrays</a></code>
                           is <tref>false</tref>, and <i>value</i> is not an
                           <tref>array</tref>, set <i>value</i> to a new