Incomplete regular expression for hostnames

[wangli1030]

in internal/versionchecker/fromservice.go:28
var imageVersion = regexp.MustCompile(``^quay.io/jetstack/cert-manager-webhook:(v(?:\d+)\.(?:\d+)\.(?:\d+)(?:.*))$``)
the dot before 'io' shoule be escaped, otherwise, it will have potential risk to match more hosts.

[wangli1030]

I will raise PR to fix it.