XEP-0280: move end date since I forogt to send the email

xep-0280.xml

@@ -11,7 +11,7 @@
   &LEGALNOTICE;
   <number>0280</number>
   <status>Proposed</status>
-  <lastcall>2018-02-20</lastcall>
+  <lastcall>2018-02-22</lastcall>
   <lastcall>2017-03-28</lastcall>
   <lastcall>2017-03-01</lastcall>
   <lastcall>2017-02-22</lastcall>