upper bound on SDK constraint is not good practice

[jmesserly]

Since the SDK cannot be downgraded, it is not generally a good practice to put a cap on it. When we asked for SDK constraints we promised never to put an upper bound :)

Concretely, this caused a problem for me because I couldn't use/test quiver on 0.8.x, even though in fact the feature I wanted to use worked just fine.