Update link to the spec (#37)

The runtime-keys.proposal.wintertc.org domain didn't use to work, but now it does.

Author: andreubotella

spec.html

@@ -223,7 +223,7 @@ <h1>Deprecation</h1>
 
     <emu-clause id="sec-publication-cadence">
       <h1>Publication cadence</h1>
-      <p>This Report is published on a semi-annual basis as an ECMA Technical Report at <a href="https://runtime-keys.proposal.wintercg.org/">https://runtime-keys.proposal.wintercg.org/</a>. Changes approved at TC55 plenary meetings between publication cycles can be found in the publicly-available draft maintained in the WinterTC runtime-keys repository.</p>
+      <p>This Report is published on a semi-annual basis as an ECMA Technical Report at <a href="https://runtime-keys.proposal.wintertc.org/">https://runtime-keys.proposal.wintertc.org/</a>. Changes approved at TC55 plenary meetings between publication cycles can be found in the publicly-available draft maintained in the WinterTC runtime-keys repository.</p>
     </emu-clause>
   </emu-clause>