Update Qt version used in the changes file

The version we keep binary compatibility with is the 5.9.x series,
not 5.10.x

Change-Id: I7a21dc7e4d31c64f4e6132d3bdbcba5fd3124837
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

dist/changes-5.10.0

@@ -4,7 +4,7 @@ included in this distribution. The documentation is also available online:
 
 http://doc.qt.io/qt-5/index.html
 
-The Qt version 5.10 series is binary compatible with the 5.10.x series.
+The Qt version 5.10 series is binary compatible with the 5.9.x series.
 Applications compiled for 5.9 will continue to run with 5.10.
 
 Some of the changes listed in this file include issue tracking numbers