**Apache Airflow version**: 1.10.12

**Environment**:  Centos 7 Host

- **Cloud provider or hardware configuration**: 
- **OS** (e.g. from /etc/os-release): Ubuntu 20.04 Docker Container
- **Kernel** (e.g. `uname -a`): Linux c6c6e8230c17 3.10.0-1127.18.2.el7.x86_64 #1 SMP Sun Jul 26 15:27:06 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
- **Install tools**: Docker Compose
- **Others** ?

**What happened**:

The schema file generated by MSSQLToGCSOperator specifies that a field defined as **bit** in MSSQL, is defined as **INTEGER**.  However, the JSON file defines the value as **true**/**false**.  When attempting to import into BigQuery using the GCSOperatorToBigQuery operator, the job fails:
`Error while reading data, error message: JSON parsing error in row starting at position 0: Could not convert value 'boolean_value: false' to integer. Field: manager; Value: 0`

**What you expected to happen**:

Value should be defined as **BOOLEAN** in the schema.

**How to reproduce it**:
Ensure `dbo.Customers` table has a **bit** column:

```
export_customers = MsSqlToGoogleCloudStorageOperator(
                task_id='export_customers',
                sql='SELECT * FROM dbo.Customers;',
                bucket='mssql-export',
                filename='data/customers/export.json',
                schema_filename='schemas/export.json',
                mssql_conn_id='mssql_default',
                google_cloud_storage_conn_id='google_cloud_default',
                dag=dag
            )
```
"""
        Queries MSSQL and returns a cursor of results.
        :return: mssql cursor
        """
        mssql = MsSqlHook(mssql_conn_id=self.mssql_conn_id)
        conn = mssql.get_conn()
        cursor = conn.cursor()
        cursor.execute(self.sql)
        return cursor
    def field_to_bigquery(self, field) -> dict[str, str]:
        return {
            "name": field[0].replace(" ", "_"),
            "type": self.type_map.get(field[1], "STRING"),
            "mode": "NULLABLE",
        }
    @classmethod
    def convert_type(cls, value, schema_type, **kwargs):
        """
        Takes a value from MSSQL, and converts it to a value that's safe for
        JSON/Google Cloud Storage/BigQuery.
        Datetime, Date and Time are converted to ISO formatted strings.
        """
        if isinstance(value, decimal.Decimal):
            return float(value)
        if isinstance(value, (datetime.date, datetime.time)):
            return value.isoformat()
        return value