build(deps): Depend on ron 0.7 or 0.8

[sjackman]

Depend on ron version 0.7 or 0.8 using version = ">=0.7, <0.9".

[mitsuhiko]

The problem is that this changes the snapshot formats, that's why I had to hard pin it. I'm not sure what a good solution is here.

[sjackman]

I've opened PR #421 to bump ron to version 0.8, rather than this PR which permits either version 0.7 or 0.8.

• build(deps): bump ron from 0.7 to 0.8 #421