Enabling lexical-binding broke popup-kill-ring

[adhilton]

Enabling lexical-binding (https://github.com/auto-complete/popup-el/commit/4036e5590a842390b12919473cb71654cae28783) broke popup-kill-ring. After this commit, attempting to select any item from the menu results in Symbol’s value as variable is void: menu

See https://github.com/waymondo/popup-kill-ring/issues/5