Fixes the compile-time error show below.

globals.c:44:6: error: conflicting types for ‘doSleep’; have ‘void(int)’
   44 | void doSleep(int microseconds)
      |      ^~~~~~~
In file included from globals.c:27:
globals.h:28:13: note: previous declaration of ‘doSleep’ with type ‘void(void)’
   28 | extern void doSleep();
      |             ^~~~~~~

Index: ninvaders-0.1.1/globals.h
===================================================================
--- ninvaders-0.1.1.orig/globals.h
+++ ninvaders-0.1.1/globals.h
@@ -25,7 +25,7 @@
 #ifndef GLOBALS
 #define GLOBALS
 
-extern void doSleep();
+extern void doSleep(int microseconds);
 	
 extern void showUsage();
 extern void showVersion();
Index: ninvaders-0.1.1/nInvaders.h
===================================================================
--- ninvaders-0.1.1.orig/nInvaders.h
+++ ninvaders-0.1.1/nInvaders.h
@@ -51,7 +51,7 @@ extern int level;
 extern int skill_level;
 	
 // included from globals.h
-extern void doSleep();
+extern void doSleep(int microseconds);
 extern void showUsage();
 extern void showVersion();
 extern void showGplShort();