TST: fix travis bash syntax for AND

Author: tswast

.travis.yml

@@ -42,7 +42,7 @@ install:
 script:
   - if [[ $PYTHON== '2.7' ]]; then nox -s test27 ; fi
   - if [[ $PYTHON== '3.5' ]]; then nox -s test35 ; fi
-  - if [[ $PYTHON== '3.6' && "$PANDAS" == "MASTER" ]]; then nox -s test36master ; fi
+  - if [[ $PYTHON== '3.6' ]] && [[ "$PANDAS" == "MASTER" ]]; then nox -s test36master ; fi
   - if [ -f "$REQ.conda" ]; then pip install coverage pytest pytest-cov codecov ; pytest -v --cov=pandas_gbq --cov-report xml:/tmp/pytest-cov.xml pandas_gbq ; fi
   - if [[ $COVERAGE == 'true' ]]; then nox -s coverage ; fi
   - if [[ $LINT == 'true' ]]; then nox -s lint ; fi