Bump tox minversion to 3.18.0

Since tox 3.18.0, the whitelist_externals option has been deprecated in
favor of the new allow_list_externals option[1].

This change bumps the minversion of tox so that we can replace
the deprecated option.

[1] https://github.com/tox-dev/tox/blob/master/docs/changelog.rst#v3180-2020-07-23

Change-Id: I287ce309adf5a02e9eac3a285666c23f4eeb9d36

1 files changed, 2 insertions, 2 deletions

diff --git a/tox.ini b/tox.ini
index 1e3b7be..a58c941 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 envlist = pypy,py39,pep8
 ignore_basepython_conflict = true
-minversion = 3.1.0
+minversion = 3.18.0
 skipsdist = True
 
 [testenv]
@@ -14,7 +14,7 @@ deps =
        -r{toxinidir}/test-requirements.txt
 commands = find . -type f -name "*.py[c|o]" -delete
            stestr run --slowest {posargs}
-whitelist_externals = find
+allowlist_externals = find
 
 [testenv:debug]
 commands = oslo_debug_helper -t heatclient/tests {posargs}