Removed the "MUST" for error conditions

Author: iherman

index.html

@@ -4775,12 +4775,12 @@ <h3>Problem Details</h3>
           </dd>
           <dt>title</dt>
           <dd>
-The `title` [=property=] MUST be present and its value SHOULD provide a short
+The `title` [=property=] SHOULD provide a short
 but specific human-readable string for the problem.
           </dd>
           <dt>detail</dt>
           <dd>
-The `detail` [=property=] MUST be present and its value SHOULD provide a
+The `detail` [=property=] SHOULD provide a
 longer human-readable string for the problem.
           </dd>
         </dl>