Compatibility with Node 12

[rj-david]

Hiredis does not compile properly in node 12

[dustinblackman]

Here's an example output of a build fail when you attempt to install hiredis with Node 12.6.0.

https://gist.github.com/dustinblackman/1205c3e79a918a58d361fbadf4c048c7

[pzrq]

@rj-david @dustinblackman As others have noted, this is the C language hiredis.

It looks like hiredis-node is currently looking for a maintainer.

[yosiat]

Added support for node 12 in this PR - redis/hiredis-node#144
Hopefully, someone will look at it.