Fix moto issue on travis

.travis.yml

@@ -39,6 +39,8 @@ env:
   global:
     - PYTHONUNBUFFERED=True
     - COVERALLS_PARALLEL=true
+    # https://github.com/travis-ci/travis-ci/issues/7940
+    - BOTO_CONFIG=/dev/null
 before_install:
     - openssl aes-256-cbc -K $encrypted_b3fcf6d0737c_key -iv $encrypted_b3fcf6d0737c_iv
             -in credentials.tar.gz.enc -out credentials.tar.gz -d