add --insecure/-k flag to allow insecure requests

[stormsweeper]

The flags are based on the same ones in cURL. With the flag added, it will create an https agent that does not reject bad certificates.

fix #143

[stormsweeper]

Before:

% gq https://hasura.local/v1/graphql -H "X-Hasura-Admin-Secret: hasura" --introspect > foo.schema
Executing query... error
Error:  { errors: [ { message: 'failed to fetch' } ] }

After:

% gq https://hasura.local/v1/graphql -H "X-Hasura-Admin-Secret: hasura" --introspect -k > foo.schema
Executing query... done