Geoip filter plugin does not handle spaces in key name

[TonyLeeVT]

Good day, per the thread here, I am opening an issue.

It appears that the geoip logstash filter does not like a space in the key name.

• Version: 6.4.2
• Operating System: Ubuntu 16.04
• Config File Snippet:

Results in a _geoip_lookup_failure:
geoip {
source => "Source IP"
}

Parses just fine:
geoip {
source => "source_ip"
}

Thanks for your time.