Fixes error in install due to missing directory separator.
>>> Install mail-filter/dovecot-antispam-9999 into /var/tmp/portage/mail-filter/dovecot-antispam-9999/image
make -j4 DESTDIR=/var/tmp/portage/mail-filter/dovecot-antispam-9999/image INSTALLDIR=usr/lib64/dovecot install
Installation directory /var/tmp/portage/mail-filter/dovecot-antispam-9999/imageusr/lib64/dovecot/ doesn't exist,
run make install INSTALLDIR=...
make: *** [Makefile:64: checkinstalldir] Error 2
* ERROR: mail-filter/dovecot-antispam-9999::hering-overlay failed (install phase):
* emake failed
*
* If you need support, post the output of `emerge --info '=mail-filter/dovecot-antispam-9999::hering-overlay'`,
* the complete build log and the output of `emerge -pqv '=mail-filter/dovecot-antispam-9999::hering-overlay'`.
* The complete build log is located at '/var/tmp/portage/mail-filter/dovecot-antispam-9999/temp/build.log'.
* The ebuild environment file is located at '/var/tmp/portage/mail-filter/dovecot-antispam-9999/temp/environment'.
* Working directory: '/var/tmp/portage/mail-filter/dovecot-antispam-9999/work/dovecot-antispam-9999'
* S: '/var/tmp/portage/mail-filter/dovecot-antispam-9999/work/dovecot-antispam-9999'
Fixes error in install due to missing directory separator.