EMQ fails to start if run under a different linux user than that which first ran it (emqttd#842)

Depend on goldrush and emqtt/pbkdf2 to resolve the building errors (emqttd#956)

Compile error in v2.1.0-beta.2 (emq-relx#32)

Change the default storage_type to ‘ram’ (emq-retainer#13)