[gatsby-transformer-sharp] Remove the default width value from gatsby-transformer-sharp

[Windvis]

Summary

In this commit (which was released in gatsby 2.0.0-rc.0) the requirement of a width value was removed. I believe this should make it possible to set a height, and make sharp calculate the width of the image. The problem is that gatsby-transformer-sharp still has the default values set, so using those methods in a query still results in the width being set to 400 (the default).

It would be awesome if gatsby-transformer-sharp was also updated with these changes.

Motivation

I'm trying to create a portfolio website with an image grid which needs all images to be of the same height and width being variable, but as far as I know this is not yet possible with the current implementation.

[Windvis]

I can take a look at this. Should I just remove the default values? Should there be some validation on the arguments? (Width or height should be set for example) I'm fairly new to GraphQl so I'm not sure if that is something that is done in practise.