**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
"""Forces removal of providers in editable mode."""
    def run(self):
        self.announce('Installing in editable mode. Uninstalling provider packages!', level=log.INFO)
        
        
        
        try:
            installed_packages = (
                subprocess.check_output(["python3", "-m", "pip", "freeze"]).decode().splitlines()
            )
            airflow_provider_packages = [
                package_line.split("=")[0]
                for package_line in installed_packages
                if package_line.startswith("apache-airflow-providers")
            ]
            self.announce(f'Uninstalling ${airflow_provider_packages}!', level=log.INFO)
            subprocess.check_call(["python3", "-m", "pip", "uninstall", "--yes", *airflow_provider_packages])
        except subprocess.CalledProcessError as e:
            self.announce(f'Error when uninstalling airflow provider packages: {e}!', level=log.WARN)
        super().run()
class Install(install_orig):