Change scripts['server'] to ['start']

>npm WARN feathericon@1.0.0-beta.2 scripts['server'] should probably be scripts['start'].
>https://travis-ci.org/feathericon/feathericon/jobs/401389700#L2711

https://github.com/feathericon/feathericon/blob/aad3dec41b353ec09ca257b124e2aee80e1cecff/package.json#L14