**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
            )
```
op = MSSQLToGCSOperator(
            task_id=TASK_ID,
            mssql_conn_id=MSSQL_CONN_ID,
            sql=SQL,
            bucket=BUCKET,
            filename=JSON_FILENAME,
        )
        assert op.convert_type(value, None) == expected
    def test_init(self):
        """Test MySqlToGoogleCloudStorageOperator instance is properly initialized."""
        op = MSSQLToGCSOperator(task_id=TASK_ID, sql=SQL, bucket=BUCKET, filename=JSON_FILENAME)
        assert op.task_id == TASK_ID
        assert op.sql == SQL
        assert op.bucket == BUCKET
        assert op.filename == JSON_FILENAME
    @mock.patch("airflow.providers.google.cloud.transfers.mssql_to_gcs.MsSqlHook")
    @mock.patch("airflow.providers.google.cloud.transfers.sql_to_gcs.GCSHook")
    def test_exec_success_json(self, gcs_hook_mock_class, mssql_hook_mock_class):