Update .travis.yml

.travis.yml

@@ -1,14 +1,19 @@
 language: python
 python:
+  - "2.6"
+  - "2.7"
   - "3.2"
   - "3.3"
   - "3.4"
   - "3.5"
+  - "3.5-dev" # 3.5 development branch
   - "3.6"
-  - "3.6-dev"
-
-install: 
-  - if [ "$TRAVIS_PYTHON_VERSION" == "3.2" ]; then travis_retry pip install coverage==3.7.1; fi
-  - if [ "$TRAVIS_PYTHON_VERSION" != "3.2" ]; then travis_retry pip install coverage; fi
-  - "pip install pytest pytest-cov"
-script: py.test --doctest-modules --cov ./
+  - "3.6-dev" # 3.6 development branch
+  - "3.7-dev" # 3.7 development branch
+  - "nightly"
+
+install:
+  - pip install -r requirements.txt
+
+script:
+  - py.test