Drop 3.9 from TravisCI config

Looks like TravisCI doesn't have a nightly Python 3.9 build yet, so
remove that for now.

.travis.yml

@@ -10,10 +10,6 @@ script:
   - travis_wait 60 tox
 
 matrix:
-  allow_failures:
-    - python: nightly
-    - env: PYENV_VERSION=3.9-dev TOXENV=py39
-    - env: PYENV_VERSION=3.9-dev TOXENV=py39 USE_UVLOOP=1
   fast_finish: true
   include:
     - os: linux
@@ -46,16 +42,6 @@ matrix:
       dist: xenial
       python: 3.8
       env: TOXENV=py38 USE_UVLOOP=1
-    - os: linux
-      sudo: required
-      dist: xenial
-      python: nightly
-      env: TOXENV=py39
-    - os: linux
-      sudo: required
-      dist: xenial
-      python: nightly
-      env: TOXENV=py39 USE_UVLOOP=1
     - os: osx
       osx_image: xcode9.4
       language: generic
@@ -80,11 +66,3 @@ matrix:
       osx_image: xcode11.2
       language: generic
       env: PYENV_VERSION=3.8-dev TOXENV=py38 USE_UVLOOP=1
-    - os: osx
-      osx_image: xcode11.2
-      language: generic
-      env: PYENV_VERSION=3.9-dev TOXENV=py39
-    - os: osx
-      osx_image: xcode11.2
-      language: generic
-      env: PYENV_VERSION=3.9-dev TOXENV=py39 USE_UVLOOP=1