update travis-ci to take latest pyexcel-io

Author: chfw

.travis.yml

@@ -9,6 +9,7 @@ python:
   - 3.4
 install:
   - pip install git+https://github.com/chfw/ezodf.git
+  - pip install git+https://github.com/chfw/pyexcel-io.git
   - pip install git+https://github.com/chfw/pyexcel.git
   - pip install -r requirements.txt --use-mirrors
   - pip install -r tests/requirements.txt --use-mirrors