fix: update postcss config path to root directory

Author: EricGusmao

Diff for: lib/tailwindcss/commands.rb

@@ -14,7 +14,7 @@ def compile_command(debug: false, **kwargs)
 
         command << "--minify" unless (debug || rails_css_compressor?)
 
-        postcss_path = rails_root.join("config/postcss.config.js")
+        postcss_path = rails_root.join("postcss.config.js")
         command += ["--postcss", postcss_path.to_s] if File.exist?(postcss_path)
 
         command

Diff for: test/lib/tailwindcss/commands_test.rb

@@ -57,8 +57,7 @@ def setup
         assert_equal(executable, actual.first)
         refute_includes(actual, "--postcss")
 
-        config_file = Rails.root.join("config/postcss.config.js")
-        FileUtils.mkdir_p(Rails.root.join("config"))
+        config_file = Rails.root.join("postcss.config.js")
         FileUtils.touch(config_file)
         actual = Tailwindcss::Commands.compile_command
         assert_kind_of(Array, actual)