Fix the agreement issue the other way.

Plural works better with the previous sentence. The agreement problem
was there in my original commit. I was just confused by the half
that Tim promoted.

doc/draft-terriberry-oggopus.xml

@@ -813,8 +813,8 @@ No terminating NUL octet is required.
 <vspace blankLines="1"/>
 This tag is intended to identify the codec encoder and encapsulation
  implementations, for tracing differences in technical behavior.
-The user-facing encoding application can use the 'ENCODER' user commment tag
- name to identify itself.
+User-facing encoding applications can use the 'ENCODER' user comment tag
+ to identify themselves.
 <vspace blankLines="1"/>
 </t>
 <t><spanx style="strong">User Comment List Length</spanx> (32 bits, unsigned,