work around failing to start nerves_key when optional dep

lib/nerves_hub_link/application.ex

@@ -11,6 +11,8 @@ defmodule NervesHubLink.Application do
   }
 
   def start(_type, _args) do
+    _ = maybe_start_nerves_key()
+
     config = Configurator.build()
 
     children =
@@ -32,4 +34,18 @@ defmodule NervesHubLink.Application do
       children
     end
   end
+
+  defp maybe_start_nerves_key() do
+    if Code.ensure_loaded?(NervesKey) do
+      # Because :nerves_key is an optional dep, it does not get added to
+      # .app resource files or may be started in the wrong order
+      # causing failures when calling code that is not yet started.
+      # So we explicitly tell the :nerves_key to start here to ensure
+      # its available when needed. This can be removed once the fix
+      # has been released
+      #
+      # See https://github.com/erlang/otp/pull/2675
+      Application.ensure_all_started(:nerves_key)
+    end
+  end
 end