fix dev pandas builds

Author: shoyer

.travis.yml

@@ -34,7 +34,7 @@ matrix:
   - python: 2.7
     env: UPDATE_ENV="pip install toolz https://github.com/blaze/dask/archive/master.zip"
   - python: 2.7
-    env: UPDATE_ENV="conda remove pandas && pip install https://github.com/pydata/pandas/archive/master.zip"
+    env: UPDATE_ENV="conda remove pandas && conda install cython && pip install https://github.com/pydata/pandas/archive/master.zip"
   allow_failures:
   - python: 2.7
     env: UPDATE_ENV="pip install pydap"
@@ -48,7 +48,7 @@ matrix:
   - python: 2.7
     env: UPDATE_ENV="pip install toolz https://github.com/blaze/dask/archive/master.zip"
   - python: 2.7
-    env: UPDATE_ENV="conda remove pandas && pip install https://github.com/pydata/pandas/archive/master.zip"
+    env: UPDATE_ENV="conda remove pandas && conda install cython && pip install https://github.com/pydata/pandas/archive/master.zip"
 
 before_install:
   - if [[ "$TRAVIS_PYTHON_VERSION" == "2.7" ]]; then