rm temp GCM servers URL, close web-push-libs#7

GCM servers seem to have been updated

you can use url-safe base64 encoded keys, close web-push-libs#13

Merge pull request web-push-libs#1 from Minishlink/payload

Payload support with Firefox 46+ and Chrome 50+

Merge pull request web-push-libs#4 from Minishlink/TTL

Always include TTL header, fix web-push-libs#3

fix flush reset queue

fix new API in README

add build status