Update min version of tox to use allowlist
The min version of tox is updated to 3.18.0 to replace whitelist_externals
with allowist_externals option [1]
[1] https://github.com/tox-dev/tox/blob/master/docs/changelog.rst#v3180-2020-07-23
Change-Id: I3715bdc7079d6a8754be514a2131a3dae06769c2
diff --git a/tox.ini b/tox.ini
index 65b5243..032d6b7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
[tox]
-minversion = 3.9.0
+minversion = 3.18.0
envlist = pep8
skipsdist = True
ignore_basepython_conflict=true
@@ -41,7 +41,7 @@
[testenv:pdf-docs]
deps = {[testenv:docs]deps}
-whitelist_externals = make
+allowlist_externals = make
commands = sphinx-build -b latex doc/source doc/build/pdf
make -C doc/build/pdf