TST: add global pyenv so binaries appear with right aliases.

Author: tswast

.travis.yml

@@ -1,10 +1,6 @@
 sudo: false
 
 language: python
-python:
-  - "2.7"
-  - "3.5"
-  - "3.6"
 
 env:
   - PYTHON=2.7 PANDAS=0.19.2 COVERAGE='false' LINT='true'
@@ -17,6 +13,10 @@ before_install:
   - source ci/travis_process_gbq_encryption.sh
 
 install:
+  # work around https://github.com/travis-ci/travis-ci/issues/8363
+  # https://github.com/pre-commit/pre-commit/commit/e3ab8902692e896da9ded42bd4d76ea4e1de359d
+  - pyenv install $PYTHON
+  - pyenv global system $PYTHON
   - REQ="ci/requirements-${PYTHON}-${PANDAS}" ;
     if [ -f "$REQ.pip" ]; then
       pip install --upgrade nox-automation ;