Upgrading Gaspar Vardanyan's scratchpad patch to the 20200510 version.

https://github.com/GasparVardanyan/dwm-scratchpad/blob/master/dwm-scratchpad-20200510-f09418b.diff

patch/scratchpad_alt_1.h

@@ -1,3 +1,5 @@
+# define SCRATCHPAD_MASK (1u << sizeof tags / sizeof * tags)
+
 static void scratchpad_hide ();
 static _Bool scratchpad_last_showed_is_killed (void);
 static void scratchpad_remove ();