Allow URL schema resolving with rustls

[jqnatividad]

Hi @Stranger6667,
I'm also using jsonschema-rs as a library, and needed to use rustls with URL schemas, as cross no longer bundles openssl which native-tls requires.

As per the README, I explicitly enabled reqwest and rustls and disabled native-tls via default-features = false in my Cargo.toml file but I still got the compilation error.

jsonschema = { version = "0.15.1", features = [
    "resolve-file",
    "reqwest",
    "rustls"
], default-features = false }

Compiling jsonschema v0.15.1
error: the `reqwest` feature does not enable HTTP schema resolving anymore, use the `resolve-http` feature instead
  --> C:\Users\jsmith\.cargo\registry\src\github.com-1ecc6299db9ec823\jsonschema-0.15.1\src\resolver.rs:81:21
   |
81 | ...   compile_error!("the `reqwest` feature does not enable HTTP schema resolving anymore, use the `resolve-http` feature instead");

I had to tweak the conditional compilation directives to get it to work.

Fixes #353

[codecov]

Codecov Report

Merging #355 (38e8c27) into master (044935d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #355   +/-   ##
=======================================
  Coverage   82.72%   82.72%           
=======================================
  Files          57       57           
  Lines        5533     5533           
=======================================
  Hits         4577     4577           
  Misses        956      956           

Impacted Files	Coverage Δ
jsonschema/src/resolver.rs	86.95% <ø> (ø)

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[Stranger6667]

Hi @jqnatividad !

Thank you, and sorry for not getting back to you in #353! I overlooked it :(