Default dump format should be changed for Python SDK

[woop]

Expected Behavior

When using the Python SDK to dump an "Importer" to a YAML file, the type should be "file.csv"

Current Behavior

Using the dump method results in the importer's type being saved as "file", which fails validation when using the YAML file for importing from the CLI.

Steps to reproduce

Follow the current Quickstart here

Dump the importer after it is defined.

importer.dump('out.yaml')

Specifications

• Version: 0.0.1
• Platform: Ubuntu 18.04
• Subsystem:

Possible Solution

This default probably needs to be changed:
https://github.com/gojek/feast/blob/master/sdk/python/feast/sdk/importer.py#L121

[woop]

Not sure about intended behavior, which is why I created the issue.