update most deps, notably including reqwest

Fixes #60

The reqwest dependency is significant because the old version required
an old version of openssl, complicating compilation on newer platforms.
reqwest also pulled in old/duplicate versions of hyper, tokio, etc.
Nice to drop a lot of that cruft.

I left rusqlite and uuid alone because they had breaking changes I
didn't want to mess with at the moment.

Bumped the minimum Rust version to 1.30.0, as required by the
new encoding_rs crate (and perhaps other things).

src/web.rs

@@ -621,7 +621,7 @@ mod bench {
         let client = reqwest::Client::new();
         let mut f = || {
             let mut resp = client.get(url.clone()).send().unwrap();
-            assert_eq!(resp.status(), reqwest::StatusCode::Ok);
+            assert_eq!(resp.status(), reqwest::StatusCode::OK);
             buf.clear();
             use std::io::Read;
             resp.read_to_end(&mut buf).unwrap();