Add Elixir to the list of language bindings

Summary: Closes https://github.com/facebook/rocksdb/pull/3183

Differential Revision: D6386140

Pulled By: maysamyabandeh

fbshipit-source-id: ca71d54edd741c3b7d9676ee2bcf584a5d49bc35

LANGUAGE-BINDINGS.md

@@ -14,3 +14,4 @@ This is the list of all known third-party language bindings for RocksDB. If some
     * https://github.com/bh1xuw/rust-rocks
 * D programming language - https://github.com/b1naryth1ef/rocksdb
 * Erlang - https://gitlab.com/barrel-db/erlang-rocksdb
+* Elixir - https://github.com/urbint/rox