Add support for Gatsby V5

[gdams]

Now that Gatsby 5.0.0 is available, it would be good if this plugin could be updated to avoid the following warning:

warn Plugin gatsby-plugin-react-svg is not compatible with your gatsby version 5.0.0 - It requires gatsby@^4.0.0 || ^3.0.0 || ^2.0.0

Thanks, let me know if I can do anything to help?

[tsamantanis]

Created #55 to fix this let's hope it gets merged soon.

[samuel99]

@jacobmischka Can this be merged?

[gdams]

Looks like this is now resolved in 3.3.0, thank you!