NEWS: add v3.0.7

[gyuho]

/cc @heyitsanthony @xiang90

Anything else to backport?

##### Bug fixes

- [GH6253](https://github.com/coreos/etcd/pull/6253): discovery: reject IP address records in SRVGetCluster
- [GH6267](https://github.com/coreos/etcd/pull/6267): wal: fix CRC corruption on writes following write tears
- [GH6309](https://github.com/coreos/etcd/pull/6309): etcdserver: allow zero kv index for cluster upgrade
- [GH6310](https://github.com/coreos/etcd/pull/6310): wal: use page buffered writer for writing records

[heyitsanthony]

#6284 and #6269?

[gyuho]

Ok just backported.

[xiang90]

lgtm

[gyuho]

@heyitsanthony Let's do release this afternoon. Hopefully we can include patches for quote-parsing bug in etcdctl.