Fix pandas-gbq deps (#25912)

Author: h-vetinari

ci/deps/travis-36-cov.yaml

@@ -19,6 +19,9 @@ dependencies:
   - pandas-gbq
   - psycopg2
   - pyarrow=0.9.0
+  # add pydata-google-auth until for pandas-gbq, see
+  # https://github.com/conda-forge/pandas-gbq-feedstock/issues/18
+  - pydata-google-auth
   - pymysql
   - pytables
   - python-snappy