fabric: modernize

Using doc:
https://github.com/Homebrew/homebrew/blob/master/share/doc/homebrew/Python-for-Formula-Authors.md

Closes Homebrew/legacy-homebrew#35751.

Signed-off-by: Tim D. Smith <git@tim-smith.us>

Formula/fabric.rb

@@ -30,16 +30,18 @@ class Fabric < Formula
   end
 
   def install
-    ENV.prepend_create_path "PYTHONPATH", libexec + "lib/python2.7/site-packages"
-    ENV.prepend_create_path "PYTHONPATH", prefix + "lib/python2.7/site-packages"
-
+    ENV.prepend_create_path "PYTHONPATH", libexec/"vendor/lib/python2.7/site-packages"
     resources.each do |r|
-      r.stage { system "python", "setup.py", "install", "--prefix=#{libexec}" }
+      r.stage do
+        system "python", *Language::Python.setup_install_args(libexec/"vendor")
+      end
     end
 
-    system "python", "setup.py", "install", "--prefix=#{libexec}"
+    ENV.prepend_create_path "PYTHONPATH", libexec/"lib/python2.7/site-packages"
+    system "python", *Language::Python.setup_install_args(libexec)
 
-    (bin/"fab").write_env_script libexec/"bin/fab", :PYTHONPATH => ENV["PYTHONPATH"]
+    bin.install Dir[libexec/"bin/*"]
+    bin.env_script_all_files(libexec/"bin", :PYTHONPATH => ENV["PYTHONPATH"])
   end
 
   test do