Use the Config module instead of Mix.Config is deprecated

Gets rid of:
warning: use Mix.Config is deprecated. Use the Config module instead
  config/config.exs:3

Author: joustava

config/config.exs

@@ -1,6 +1,6 @@
 # This file is responsible for configuring your application
-# and its dependencies with the aid of the Mix.Config module.
-use Mix.Config
+# and its dependencies with the aid of the Config module.
+import Config
 
 # This configuration is loaded before any dependency and is restricted
 # to this project. If another project depends on this project, this
@@ -27,4 +27,4 @@ use Mix.Config
 # Configuration from the imported file will override the ones defined
 # here (which is why it is important to import them last).
 #
-#     import_config "#{Mix.env()}.exs"
+#     import_config "#{config_env()}.exs"

mix.lock

@@ -0,0 +1,3 @@
+%{
+  "uf2tool": {:hex, :uf2tool, "1.1.0", "7091931234ca5a256b66ea691983867d51229798622d083f85c1ad779798a734", [:rebar3], [], "hexpm", "1a7e5ca7ef3d19c7a0b0acf3db804b3188e0980884acffa13fd57d733507b73d"},
+}