Fix unclosed dfn tags in WebCodecs spec (#875)

* Fix unclosed dfn tags in WebCodecs spec

* Fix one more end tag typo.

Author: dalecurtis

index.src.html

@@ -499,7 +499,7 @@
     {{AbortError}} {{DOMException}}.
   </dd>
 
-  <dt><dfn method for=AudioDecoder>close()</df></dt>
+  <dt><dfn method for=AudioDecoder>close()</dfn></dt>
   <dd>
     Immediately aborts all pending work and releases [=system resources=].
     Close is final.
@@ -845,7 +845,7 @@
     {{AbortError}} {{DOMException}}.
   </dd>
 
-  <dt><dfn method for=VideoDecoder>close()</df></dt>
+  <dt><dfn method for=VideoDecoder>close()</dfn></dt>
   <dd>
     Immediately aborts all pending work and releases [=system resources=].
     Close is final.
@@ -1184,7 +1184,7 @@
     {{AbortError}} {{DOMException}}.
   </dd>
 
-  <dt><dfn method for=AudioEncoder>close()</df></dt>
+  <dt><dfn method for=AudioEncoder>close()</dfn></dt>
   <dd>
     Immediately aborts all pending work and releases [=system resources=].
     Close is final.
@@ -1560,7 +1560,7 @@
     {{AbortError}} {{DOMException}}.
   </dd>
 
-  <dt><dfn method for=VideoEncoder>close()</df></dt>
+  <dt><dfn method for=VideoEncoder>close()</dfn></dt>
   <dd>
     Immediately aborts all pending work and releases [=system resources=].
     Close is final.
@@ -5344,7 +5344,7 @@
 :: A boolean indicating whether {{ImageDecoder/[[encoded data]]}} is completely
     buffered.
 
-: <dfn attribute for=ImageDecoder>[[completed promise]]</dnf>
+: <dfn attribute for=ImageDecoder>[[completed promise]]</dfn>
 :: The promise used to signal when {{ImageDecoder/[[complete]]}} becomes
     `true`.