Add SQLAlchemy 0.9 to test matrix

.travis.yml

@@ -7,7 +7,14 @@ python:
   - 2.6
   - 2.7
   - 3.3
+
+env:
+  matrix:
+    - SQLALCHEMY=SQLAlchemy==0.9
+    - SQLALCHEMY=SQLAlchemy==0.8.4
+
 install:
+  - "pip install $SQLALCHEMY"
   - pip install -e ".[test]"
 script:
   - python setup.py test