fix(lockfile): ensure newline at EOF for lockfile

Text files should end with a newline. This also lets you manually edit
the lockfile in vim without 'fixeol' creating a spurious change for the
added newline.

This change however will create a change in users' lockfiles adding a
newline upon updating, but since the lockfile would be changing anyways
to update lazy.nvim itself, this is likely acceptable.

lua/lazy/manage/lock.lua

@@ -42,7 +42,7 @@ function M.update()
       f:write(",\n")
     end
   end
-  f:write("\n}")
+  f:write("\n}\n")
   f:close()
 end