BREAKING CHANGE:

1. We now require Node.js v10.12.0 or newer.
2. We now only work with Redis v3.0.0 or newer.
3. `Redis` can't be called as a function anymore as it's now a class.
Please change `Redis()` to `new Redis()`. Note that `Redis()` was already deprecated
in the previous version.

BREAKING CHANGE: Related methods are kept but they don't take any effects.

The native Promise will always be used.

…connect of redis

The happy case should be slightly faster that way when there are multiple arguments

Closes #1293

BREAKING CHANGE: `Redis#serverInfo` is removed. This field is never documented so
you very likely have never used it.

BREAKING CHANGE: `allowUsernameInURI` is removed and ioredis will always
use the username passed via URI.

Previously, the `username` part in `new Redis("redis://username:authpassword@127.0.0.1:6380/4")`
was ignored unless `allowUsernameInURI` is specified: `new Redis("redis://username:authpassword@127.0.0.1:6380/4?allowUsernameInURI=true")`.

Now, if you don't want to send username to Redis, just leave the username part empty:
`new Redis("redis://:authpassword@127.0.0.1:6380/4")`

…on for mixed buffer and text based commands

BREAKING CHANGE: `slotsRefreshInterval` is disabled by default,
previously, the default value was 5000.