xfce-do-release: match multiple spaces for git version replace

Makes 'xfce-do-release' as well usable for xfwm4, which has some more
spaces in the line: 'm4_define([xfwm4_version_tag],   [git])'

MR !74

helpers/xfce-do-release

@@ -217,10 +217,10 @@ update_configure_ac_in () {
 				-e "s/^\(m4_define(\[.*_version_major\].* \[\)\(.*\)\(\])\)/\1$version_major\3/g" \
 				-e "s/^\(m4_define(\[.*_version_minor\].* \[\)\(.*\)\(\])\)/\1$version_minor\3/g" \
 				-e "s/^\(m4_define(\[.*_version_micro\].* \[\)\(.*\)\(\])\)/\1$version_patch\3/g" \
-				-e 's/^\(m4_define(\[.*_version_tag\], \[\)\(git\)\(\])\)/\1\3/g' \
+				-e 's/^\(m4_define(\[.*_version_tag\],* \[\)\(git\)\(\])\)/\1\3/g' \
 				"$configure_file"
 		elif [ "$1" = "post" ]; then
-			sed -i 's/\(m4_define(\[.*_version_tag\], \[\)\(.*\)\(\])\)/\1git\3/g' "$configure_file"
+			sed -i 's/\(m4_define(\[.*_version_tag\],* \[\)\(.*\)\(\])\)/\1git\3/g' "$configure_file"
 		fi
 	fi