- Fixed installation script from Makefile.am

Hello,

Just noticed installation script will fail if easyrsadir does not exist prior. Amended Makefile.am accordingly. Now RPM package creation builds seamlessly from:
autoreconf -i
./configure --prefix=/usr
make dist-gzip
rpmbuild -ta easy-rsa-....tar.gz

Great work with easy-rsa, congratulations.

Best regards,

Chris