Fix the makefile ('[[' is bash-specific, 'rm -f' don't remove directories)

git-svn-id: https://nagiosplug.svn.sourceforge.net/svnroot/nagiosplug/nagiosplug/trunk@1623 f882894a-f735-0410-b71e-b25c423dba1c

doc/makefile

@@ -2,9 +2,9 @@
 
 developer-guidelines.html: developer-guidelines.sgml
 	docbook2html -u developer-guidelines.sgml
-	if [[ -e developer-guidelines/developer-guidelines.html ]] ; then \
+	if [ -e developer-guidelines/developer-guidelines.html ] ; then \
 		mv developer-guidelines/developer-guidelines.html . ;\
-		rm -f developer-guidelines ;\
+		rm -rf developer-guidelines ;\
 	fi
 
 clean: