[CHANGELOG] Add glium update

Include a word about WINIT_HIDPI_FACTOR=1.

Author: malikolivier

CHANGELOG.markdown

@@ -41,6 +41,9 @@
   Keep redirection.
   - Rename `ImGuiCol::ChildWindowBg` to `ImGuiCol::ChildBg`.
   Keep redirection.
+- Upgrade glium to 0.22.0. This updates winit to 0.16. This changes the way
+HIDPI are calculated. Depending on your needs, you may want to set HIDPI to 1
+by setting the environment variable `WINIT_HIDPI_FACTOR=1` if you use X11.
 
 ### Deprecated