applied the fix inspired by a recent wmii commit

Makefile

@@ -44,7 +44,7 @@ install: all
 	@chmod 755 ${DESTDIR}${PREFIX}/bin/dmenu
 	@echo installing manual page to ${DESTDIR}${MANPREFIX}/man1
 	@mkdir -p ${DESTDIR}${MANPREFIX}/man1
-	@sed 's/VERSION/${VERSION}/g' < dmenu.1 > ${DESTDIR}${MANPREFIX}/man1/dmenu.1
+	@sed "s/VERSION/${VERSION}/g" < dmenu.1 > ${DESTDIR}${MANPREFIX}/man1/dmenu.1
 	@chmod 644 ${DESTDIR}${MANPREFIX}/man1/dmenu.1
 
 uninstall: