Only install pytest-asyncio in supported builds

Author: nocarryr

.travis.yml

@@ -2,19 +2,26 @@ language: python
 matrix:
     include:
     - python: "2.7"
-      env: ALLOW_DEPLOY=false
+      env:
+          - ALLOW_DEPLOY=false
+          - AIO_AVAILABLE=false
     - python: "3.4"
-      env: ALLOW_DEPLOY=false
+      env:
+          - ALLOW_DEPLOY=false
+          - AIO_AVAILABLE=false
     - python: "3.5"
-      env: ALLOW_DEPLOY=true
+      env:
+          - ALLOW_DEPLOY=true
+          - AIO_AVAILABLE=true
 addons:
   apt:
     packages:
       - pandoc
 install:
   - pip install -U pip setuptools wheel
   - sh -c "if [ '$ALLOW_DEPLOY' = 'true' ]; then pip install -r doc/requirements.txt & pip install travis-sphinx; fi"
-  - pip install -U pytest pytest-asyncio pytest-cov coveralls pypandoc
+  - pip install -U pytest pytest-cov coveralls pypandoc
+  - sh -c "if [ '$AIO_AVAILABLE' = 'true' ]; then pip install -U pytest-asyncio; fi"
   - pip install -e .
 script:
   - sh -c "if [ '$ALLOW_DEPLOY' = 'true' ]; then travis-sphinx --source=doc/source --nowarn build; fi"