Unnecessary None in logged output of available Checkers

[anthonyharrison]

Erroneous None in logged output after reporting available Checkers

INFO     cve_bin_tool.VersionScanner - Checkers: avahi, bash, bind, binutils, busybox,     version_scanner.py:88
                    bzip2, cups, curl, dovecot, expat, ffmpeg, freeradius, gcc, gimp, glibc, gnutls,                      
                    gstreamer, haproxy, hostapd, icecast, icu, irssi, kerberos, libarchive, libcurl,                      
                    libdb, libgcrypt, libjpeg, libnss, libtiff, libvirt, lighttpd, mariadb,                                
                    memcached, mysql, ncurses, nessus, netpbm, nginx, node, openafs, openldap,                            
                    openssh, openssl, openswan, openvpn, png, polarssl_fedora, postgresql, python,                        
                    qt, radare2, rsyslog, samba, sqlite, strongswan, subversion, syslogng, systemd,                        
                    tcpdump, varnish, wireshark, xerces, xml2, zlib                                                        
INFO     cve_bin_tool - None         cli.py:320

[terriko]

Closed by #958