Replace the TravisCI Python 3.6 config with CircleCI Python 3.6 config

.circleci/config.yml

@@ -30,6 +30,9 @@ workflows:
       # Test against PyPy 2.7
       - "pypy2.7-buster"
 
+      # Just one Python 3.6 configuration while the port is in-progress.
+      - "python3.6"
+
       # Other assorted tasks and configurations
       - "lint"
       - "pyinstaller"
@@ -261,13 +264,20 @@ jobs:
         user: "nobody"
 
 
-  ubuntu-18.04:
+  ubuntu-18.04: &UBUNTU_18_04
     <<: *DEBIAN
     docker:
       - image: "tahoelafsci/ubuntu:18.04"
         user: "nobody"
 
 
+  python3.6:
+    <<: *UBUNTU_18_04
+    environment:
+      <<: *UTF_8_ENVIRONMENT
+      TAHOE_LAFS_TOX_ENVIRONMENT: "py36"
+
+
   centos-8: &RHEL_DERIV
     docker:
       - image: "tahoelafsci/centos:8"

.travis.yml

@@ -1,40 +0,0 @@
-sudo: false
-language: python
-cache: pip
-dist: xenial
-before_cache:
-  - rm -f $HOME/.cache/pip/log/debug.log
-git:
-  depth: 1000
-
-env:
-  global:
-    - TAHOE_LAFS_HYPOTHESIS_PROFILE=ci
-
-install:
-  - pip install --upgrade tox setuptools virtualenv
-  - echo $PATH; which python; which pip; which tox
-  - python misc/build_helpers/show-tool-versions.py
-
-script:
-  - |
-    set -eo pipefail
-    tox -e ${T}
-
-notifications:
-  email: false
-  irc:
-    channels: "chat.freenode.net#tahoe-lafs"
-    on_success: always # for testing
-    on_failure: always
-    template:
-      - "%{repository}#%{build_number} [%{branch}: %{commit} by %{author}] %{message}"
-      - "Changes: %{compare_url} | Details: %{build_url}"
-
-matrix:
-  include:
-  - os: linux
-    python: '3.6'
-    env: T=py36
-
-  fast_finish: true