Replace to-be-deprecated `std:🔚:home_dir()` with `dirs::home_dir()`

Found by building on nightly

Cargo.toml

@@ -18,6 +18,7 @@ bitcoin = "0.13"
 chan = "0.1"
 chan-signal = "0.3"
 clap = "2.31"
+dirs = "1.0"
 error-chain = "0.12"
 glob = "0.2"
 hex = "0.3"

src/config.rs

@@ -1,5 +1,5 @@
 use clap::{App, Arg};
-use std::env::home_dir;
+use dirs::home_dir;
 use std::fs;
 use std::net::SocketAddr;
 use std::path::{Path, PathBuf};

src/lib.rs

@@ -5,6 +5,7 @@ extern crate bincode;
 extern crate bitcoin;
 extern crate chan_signal;
 extern crate crypto;
+extern crate dirs;
 extern crate glob;
 extern crate hex;
 extern crate libc;