flarectl: Move api invocation to checkEnv()
flarectl: Move api invocation to checkEnv()

Since 586e5a5 `cloudflare.New()` will error if the API email and key are
not defined. Since flarectl was instantiating the API object at the
start, this meant that flarectl would not operate at all without having
the environment variables defined.

This moves the API object instantiation to `checkEnv()` so that, e.g.
`ips` and `--help` will still work. All other functions already call
`checkEnv()`.

Refs #73

cloudflare/cloudflare-go,cloudflare/cloudflare-go