fix broken blank substitution

Graph on https://xs.powerdns.com/dnssec-nl-graph/ shows emtpy data points for .cz DNSSec delegations. It seems they have not only a blank in their number they report on their website.
So a sed 's/[^0-9]//g' should do the trick.
Merge pull request #6 from stasic/patch-1

fix broken blank substitution for .cz domain count