Correctly set minimal versions for graphql_client

[DanielVoogsgerd]

Currently, the minimal version for serde_json is set incorrectly, it requires Eq to be implemented for serde_json::Value, yet this was only introduced in 1.0.50. Also removed a redundant caret in the serde dependency.

One other small consideration might be necessary for reqwest. Currently, the reqwest version is bound by >=0.11, <=0.12.
This seems odd, as in theory this would allow all of 0.11.x, but also 0.12.y. A quick test shows that Cargo refuses to select 0.12.y in this case. I am not sure if this is a bug in Cargo as well.

But to get back to this crate. If the idea is that everything in 0.11.x would be okay, but not 0.12.y the canonical way of defining this would be just 0.11.0 (or 0.11 if you want to be implicit). If 0.12.y should be selected too, I would just like to inform you that this seems to be currently unsupported by Cargo.

Never mind that last part, I was looking at 0.14 instead of main, my bad. I still think that >=0.11.0, <0.13.0 would be clearer, but that is simply preference.

[tomhoule]

Good call. I think we'll refocus the crate on just codegen, then the number of dependencies will be much lower.