docs: Fix a typo in the GVariant text format documentation

There were some quotes missing from an a{sv} key.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

docs/reference/glib/gvariant-text.xml

@@ -465,7 +465,7 @@
     parses successfully.  You would need to specify <literal>[&lt;['']&gt;, &lt;@as []&gt;]</literal>.
    </para>
    <para>
-    <literal>{"title": &lt;"frobit"&gt;, "enabled": &lt;true&gt;, width: &lt;800&gt;}</literal> is an example of
+    <literal>{"title": &lt;"frobit"&gt;, "enabled": &lt;true&gt;, "width": &lt;800&gt;}</literal> is an example of
     perhaps the most pervasive use of both dictionaries and variants.
    </para>
   </refsect2>