python@3.8: update style; update setuptools

Closes #136.

Signed-off-by: Aleks Bunin <868842+sashkab@users.noreply.github.com>

Author: sashkab

Formula/python@3.8.rb

@@ -42,8 +42,8 @@ class PythonAT38 < Formula
              "bin/easy_install-3.7", "bin/easy_install-3.8"
 
   resource "setuptools" do
-    url "https://pypi.org/packages/source/s/setuptools/setuptools-57.4.0.tar.gz"
-    sha256 "6bac238ffdf24e8806c61440e755192470352850f3419a52f26ffe0a1a64f465"
+    url "https://pypi.org/packages/source/s/setuptools/setuptools-58.0.3.tar.gz"
+    sha256 "5e4c36f55012a46c1b3e4b67a8236d1d73856a90fc7b3207d29bedb7d2bac417"
   end
 
   resource "pip" do
@@ -82,7 +82,7 @@ def install
     ENV["PYTHONPATH"] = nil
 
     # Override the auto-detection in setup.py, which assumes a universal build.
-    on_macos do
+    if OS.mac?
       ENV["PYTHON_DECIMAL_WITH_MACHINE"] = Hardware::CPU.arm? ? "uint128" : "x64"
     end