fix: improve git commit message via nvr

Switch to the BufUnload event for reopening LazyGit window, so that the
user can switch windows before submitting his commit message.

lua/lazygit.lua

@@ -224,4 +224,9 @@ local function lazygitconfig()
   end
 end
 
-return { lazygit = lazygit, lazygitfilter = lazygitfilter, lazygitconfig = lazygitconfig }
+return {
+  lazygit = lazygit,
+  lazygitfilter = lazygitfilter,
+  lazygitconfig = lazygitconfig,
+  project_root_dir = project_root_dir,
+}