[skip ci] Add note for lexbor v2.7.0 upgrade

Author: iluuu1994

NEWS

@@ -24,6 +24,7 @@ PHP                                                                        NEWS
     declarations after setAttributeNS()). (David Carlier)
   . Fixed bug GH-21688 (segmentation fault on empty HTMLDocument).
     (David Carlier)
+  . Upgrade to lexbor v2.7.0. (ndossche, ilutov)
 
 - Iconv:
   . Fixed bug GH-17399 (iconv memory leak on bailout). (iliaal)