Add neachdainn/nng-rs

NNG is the successor to Nanomsg and, given that [Nanomsg is actively recommending switching to NNG][1], it seems like it would be a good idea to have it on this list. Thanks!

[1]: https://github.com/nanomsg/nanomsg#support

README.md

@@ -1137,6 +1137,8 @@ See also [Are we game yet?](http://arewegameyet.com)
   * [actix/actix](https://github.com/actix/actix) — Actor library for Rust [<img src="https://api.travis-ci.org/actix/actix.svg?branch=master">](https://travis-ci.org/actix/actix)
 * NanoMsg
   * [thehydroimpulse/nanomsg.rs](https://github.com/thehydroimpulse/nanomsg.rs) — [nanomsg](https://nanomsg.org/) bindings [<img src="https://api.travis-ci.org/thehydroimpulse/nanomsg.rs.svg?branch=master">](https://travis-ci.org/thehydroimpulse/nanomsg.rs)
+* Nng
+  * [neachdainn/nng-rs](https://gitlab.com/neachdainn/nng-rs) [[Nng](http://crates.io/crates/nng)] — [Nng (nanomsg v2)](https://nanomsg.github.io/nng/index.html) bindings [<img src="https://gitlab.com/neachdainn/nng-rs/badges/master/pipeline.svg">](https://gitlab.com/neachdainn/nng-rs/pipelines)
 * NNTP
   * [mattnenterprise/rust-nntp](https://github.com/mattnenterprise/rust-nntp) — an [NNTP](https://en.wikipedia.org/wiki/Network_News_Transfer_Protocol) client for Rust [<img src="https://api.travis-ci.org/mattnenterprise/rust-nntp.svg?branch=master">](https://travis-ci.org/mattnenterprise/rust-nntp)
 * POP3