Add force to gzip commands

Without force make shows errors when .gz
files already exist.

Signed-off-by: Daniel Madej <daniel.madej@huawei.com>

casadm/Makefile

@@ -158,7 +158,7 @@ endif
 -include $(addprefix $(OBJDIR),$(OBJS:.o=.d))
 
 manpage:
-	gzip -k $(TARGET).8
+	gzip -k -f $(TARGET).8
 
 clean:
 	@echo "  CLEAN "