fix: tweak pyarrow extra to soothe PyPI (#230)

Release-As: 1.27.1

Author: tseaver

setup.py

@@ -47,8 +47,11 @@
     ],
     "pandas": ["pandas>=0.17.1"],
     # Exclude PyArrow dependency from Windows Python 2.7.
-    'pyarrow: platform_system != "Windows" or python_version >= "3.5"': [
-        "pyarrow>=1.0.0, <2.0dev; python_version>='3.4'",
+    'pyarrow: platform_system == "Windows"': [
+        "pyarrow>=1.0.0, <2.0dev; python_version>='3.5'",
+    ],
+    'pyarrow: platform_system != "Windows"': [
+        "pyarrow>=1.0.0, <2.0dev; python_version>='3.5'",
         # Pyarrow >= 0.17.0 is not compatible with Python 2 anymore.
         "pyarrow < 0.17.0; python_version < '3.0'",
     ],