chore: Prepare tonic v0.5.2 (#738)

So as highlighted by
https://github.com/hyperium/tonic/issues/730#issuecomment-895635088 it
turns out the new `Interceptor` trait required changes to tonic-build as
well, which I forgot to publish yesterday. Didn't see it because it wasn't
clear from the commit message.

So this bumps tonic _and_ tonic-build to 0.5.2 so we can release both.
There are no code changes.

tonic/Cargo.toml

@@ -8,11 +8,11 @@ name = "tonic"
 #   - README.md
 # - Update CHANGELOG.md.
 # - Create "v0.5.x" git tag.
-version = "0.5.1"
+version = "0.5.2"
 authors = ["Lucio Franco <[email protected]>"]
 edition = "2018"
 license = "MIT"
-documentation = "https://docs.rs/tonic/0.5.1/tonic/"
+documentation = "https://docs.rs/tonic/0.5.2/tonic/"
 repository = "https://github.com/hyperium/tonic"
 homepage = "https://github.com/hyperium/tonic"
 description = """

tonic/src/lib.rs

@@ -79,7 +79,7 @@
 #![doc(
     html_logo_url = "https://raw.githubusercontent.com/tokio-rs/website/master/public/img/icons/tonic.svg"
 )]
-#![doc(html_root_url = "https://docs.rs/tonic/0.5.1")]
+#![doc(html_root_url = "https://docs.rs/tonic/0.5.2")]
 #![doc(issue_tracker_base_url = "https://github.com/hyperium/tonic/issues/")]
 #![doc(test(no_crate_inject, attr(deny(rust_2018_idioms))))]
 #![cfg_attr(docsrs, feature(doc_cfg))]