Rename salt option to hammer home that you should not use it normally (…

…#52)

I do feel we can never win this one. React has a variable __SECRET_DOM_DO_NOT_USE_OR_YOU_WILL_BE_FIRED and I've inherited code that uses it in production. Your name works though.

lib/argon2.rb

@@ -20,7 +20,7 @@ def initialize(options = {})
       @p_cost = options[:p_cost] || 1
       raise ArgonHashFail, "Invalid p_cost" if @p_cost < 1 || @p_cost > 8
 
-      @salt_do_not_supply = options[:salt_do_not_supply]
+      @insecure_salt = options[:salt_for_testing_purposes_only]
       @secret = options[:secret]
     end
 
@@ -29,7 +29,7 @@ def create(pass)
         pass.is_a?(String)
 
       # Ensure salt is freshly generated unless it was intentionally supplied.
-      salt = @salt_do_not_supply || Engine.saltgen
+      salt = @insecure_salt || Engine.saltgen
 
       Argon2::Engine.hash_argon2id_encode(
         pass, salt, @t_cost, @m_cost, @p_cost, @secret)