kernel32: Spelling fix in a comment.

dlls/kernel32/heap.c

@@ -1273,7 +1273,7 @@ BOOL WINAPI GlobalMemoryStatusEx( LPMEMORYSTATUSEX lpmemex )
     /* FIXME: should do something for other systems */
     GetSystemInfo(&si);
     lpmemex->ullTotalVirtual  = (ULONG_PTR)si.lpMaximumApplicationAddress-(ULONG_PTR)si.lpMinimumApplicationAddress;
-    /* FIXME: we should track down all the already allocated VM pages and substract them, for now arbitrarily remove 64KB so that it matches NT */
+    /* FIXME: we should track down all the already allocated VM pages and subtract them, for now arbitrarily remove 64KB so that it matches NT */
     lpmemex->ullAvailVirtual  = lpmemex->ullTotalVirtual-64*1024;
 
     /* MSDN says about AvailExtendedVirtual: Size of unreserved and uncommitted