Fixing issue on py38

AttributeError: type object 'Callable' has no attribute '_abc_registry'

Author: awais786

.travis.yml

@@ -24,7 +24,7 @@ matrix:
   # Temporary bandaid for https://github.com/PyFilesystem/pyfilesystem2/issues/342
   allow_failures:
     - python: pypy
-    - python: pypy3.5-7.0
+    - python: pypy3.5-8.0
 
 before_install:
   - pip install -U tox tox-travis

setup.py

@@ -22,7 +22,7 @@
     "Topic :: System :: Filesystems",
 ]
 
-REQUIREMENTS = ["appdirs~=1.4.3", "pytz", "setuptools", "six~=1.10"]
+REQUIREMENTS = ["appdirs~=1.4.3", "pytz", "setuptools", "six~=1.10", "typing; python_version < '3.5'"]
 
 setup(
     author="Will McGugan",
@@ -33,7 +33,6 @@
     extras_require={
         "scandir :python_version < '3.5'": ["scandir~=1.5"],
         ":python_version < '3.4'": ["enum34~=1.1.6"],
-        ":python_version < '3.6'": ["typing~=3.6"],
         ":python_version < '3.0'": ["backports.os~=0.1"],
     },
     license="MIT",

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = {py27,py34,py35,py36,py37}{,-scandir},pypy,typecheck,lint
+envlist = {py27,py34,py35,py36,py37,py38}{,-scandir},pypy,typecheck,lint
 sitepackages = False
 skip_missing_interpreters=True