docs(CHANGES) Note FutureWarning instead of DeprecationWarning

Author: tony

CHANGES

@@ -36,7 +36,7 @@ _Future release notes will be placed here_
 
 ### Deprecations
 
-- tmux versions below 3.2a are now deprecated (#606). A `DeprecationWarning` will
+- tmux versions below 3.2a are now deprecated (#606). A `FutureWarning` will
   be emitted on first use. Support for these versions will be removed in a future
   release. Set `LIBTMUX_SUPPRESS_VERSION_WARNING=1` to suppress the warning.