Disable python 3.8-dev for now; flakes checker is broken on 3.8-dev.

.travis.yml

@@ -25,10 +25,11 @@ matrix:
       env: TEST_REQUIRE=fastimport
       dist: xenial
       sudo: true
-    - python: 3.8-dev
-      env: TEST_REQUIRE=fastimport
-      dist: xenial
-      sudo: true
+    # flakes checker fails on python 3.8-dev:
+    #- python: 3.8-dev
+    #  env: TEST_REQUIRE=fastimport
+    #  dist: xenial
+    #  sudo: true
 
 install:
   - travis_retry pip install -U pip coverage codecov flake8 $TEST_REQUIRE