vim:funcs: Call timer_start instead of executing

Fix a small but stupid bug that the result of `timer_start` (i.e. the
timer ID) was evaluated as Ex command. This would lead to a jump to the
top of the file, every time the vimrc was reloaded (i.e. when a .vim is
saved).

Use `call` instead of `execute`, to fix this.

.config/vim/vimrc.d/70-functions.vim

@@ -15,5 +15,5 @@ if (exists('+autoread') && &autoread)
 		" command line window
 		silent! checktime
 	endfunc
-	execute timer_start(1000, 'CheckTime', {'repeat': -1})
+	call timer_start(1000, 'CheckTime', {'repeat': -1})
 endif