Make the code run both on Lua 5.1 (which is the default for Neovim, and is what LuaJIT provides) and Lua 5.2+.
Error detected while processing function man#open_page[58]..<SNR>54_put_page: line 8: E5105: Error while calling lua chunk: /usr/share/nvim/runtime/lua/man.lua:165: Vim(let):E805: Using a Float as a Number