src/zabbix-agent/src/GNUmakefile: avoid .. in pathname for install line
src/zabbix-agent/src/GNUmakefile: avoid .. in pathname for install line

It is not necessary, and some combination of install-sh and
tarball packaging screws this up and the directory get installed
in /etc/zabbix_agentd.d instead of /etc/zabbix/zabbix_agentd.d for
systems with a tarball packaging.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp