**What happened**:

`pandas-gbq` released version [0.15.0](https://github.com/pydata/pandas-gbq/releases/tag/0.15.0) which broke `apache-airflow-backport-providers-google==2020.11.23`

```
../lib/python3.7/site-packages/airflow/providers/google/cloud/hooks/bigquery.py:49: in <module>
    from pandas_gbq.gbq import (
E   ImportError: cannot import name '_check_google_client_version' from 'pandas_gbq.gbq' (/usr/local/lib/python3.7/site-packages/pandas_gbq/gbq.py)
```

The fix is to pin `pandas-gpq==0.14.1`.
setup.py
"""
    Compile and build the frontend assets using yarn and webpack.
    Registered as cmdclass in setup() so it can be called with ``python setup.py compile_assets``.
    """
    description = "Compile and build the frontend assets"
    user_options: List[str] = []
    def initialize_options(self):
        """Set default values for options."""
    def finalize_options(self):
        """Set final values for options."""
    def run(self):  
        """Run a command to compile and build assets."""
        subprocess.check_call('./airflow/www/compile_assets.sh')
class ListExtras(Command):