Specify python versions in the global config instead.

Author: fermezz

.travis.yml

@@ -6,7 +6,15 @@ stages:
   if: repo = pytest-dev/pytest AND tag IS NOT present
 - name: deploy
   if: repo = pytest-dev/pytest AND tag IS present
-python: '3.7'
+python:
+  - '2.7'
+  - '3.4'
+  - '3.5'
+  - '3.6'
+  - '3.7'
+  - '3.8-dev'
+  - 'pypy'
+  - 'pypy3'
 cache: false
 
 env:
@@ -44,20 +52,14 @@ jobs:
 
     # Full run of latest (major) supported versions, without xdist.
     - env: TOXENV=py27
-      python: '2.7'
     - env: TOXENV=py37
-      python: '3.7'
 
     # Coverage tracking is slow with pypy, skip it.
     - env: TOXENV=pypy
-      python: 'pypy'
     - env: TOXENV=pypy3
-      python: 'pypy3'
 
     - env: TOXENV=py34
-      python: '3.4'
     - env: TOXENV=py35-xdist
-      python: '3.5'
 
     # Coverage for:
     # - pytester's LsofFdLeakChecker
@@ -68,9 +70,7 @@ jobs:
 
     # Specialized factors for py27.
     - env: TOXENV=py27-nobyte-numpy-xdist
-      python: '2.7'
     - env: TOXENV=py27-pluggymaster-xdist
-      python: '2.7'
 
     # Specialized factors for py37.
     # Coverage for:
@@ -81,17 +81,14 @@ jobs:
 
     # Jobs only run via Travis cron jobs (currently daily).
     - env: TOXENV=py38
-      python: '3.8-dev'
       if: type = cron
 
     - stage: baseline
     # Coverage for:
     # - _pytest.unittest._handle_skip (via pexpect).
       env: TOXENV=py27-pexpect,py27-twisted PYTEST_COVERAGE=1
-      python: '2.7'
     # Use py36 here for faster baseline.
     - env: TOXENV=py36
-      python: '3.6'
     - env: TOXENV=linting,docs,doctesting PYTEST_COVERAGE=1
       cache:
         directories:
@@ -124,10 +121,8 @@ jobs:
 matrix:
   allow_failures:
     - env: TOXENV=py38
-      python: '3.8-dev'
     # Temporary (https://github.com/pytest-dev/pytest/pull/5334).
     - env: TOXENV=pypy3-xdist
-      python: 'pypy3'
 
 before_script:
   - |