📚 Fix constants rdoc section

Without resetting to the default section, code that's loaded later may
be documented in the wrong place

Author: nevans

lib/net/imap/flags.rb

@@ -257,5 +257,6 @@ class IMAP < Protocol
     # special use is likely not to be supported.
     TRASH = :Trash
 
+    # :section:
   end
 end