Update nerves config to be more idiomatic

Author: fhunleth

config/target.exs

@@ -18,10 +18,7 @@ config :nerves_runtime, :kernel, use_system_registry: false
 # https://github.com/nerves-project/erlinit/ for more information on
 # configuring erlinit.
 
-config :nerves,
-  erlinit: [
-    hostname_pattern: "nerves-%s"
-  ]
+config :nerves, :erlinit, hostname_pattern: "nerves-%s"
 
 # Configure the device for SSH IEx prompt access and firmware updates
 #