Informix Connector not available

Referring to https://github.com/strongloop/loopback-connector-informix/issues/56

The Informix Connector is not part of the tooling.
It should be available by default so informix users can take the advantage of using loopback with their systems

Acceptance Criteria

• when running lb4 datasource, the informix connectors show up as one of the available connectors.
• update Connectors reference and any related files

Related to: strongloop/loopback-next#3714

🎆 Hacktoberfest 2020

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Bắt đầu với lệnh lb4 datasource để xem các connector hiện có được hiển thị như thế nào, sau đó xem lại tài liệu tham khảo Connectors và các tệp liên quan. Xác nhận rằng connector Informix được lệnh liệt kê và cập nhật tài liệu để connector này được đề cập; issue về connector được liên kết có thể cung cấp bối cảnh triển khai.