abuild: detect /bin/sh dependency even if shebang has spaces

fixes !7

abuild.in

@@ -1004,7 +1004,7 @@ prepare_metafiles() {
 		for i in $install $triggers; do
 			local s=${i%=*}
 			[ "$name" != "${s%.*}" ] && continue
-			if head -n 1 "$startdir/$s" | grep '^#!/bin/sh' >/dev/null ; then
+			if head -n 1 "$startdir/$s" | grep -E '^#!\s*/bin/sh' >/dev/null ; then
 				msg "Script found. /bin/sh added as a dependency for $pkg"
 				deps="$deps /bin/sh"
 				break