chore: update prost, and related crates, to 0.8 (#703)

* chore: update prost, and related crates, to 0.8

Updates prost, prost-derive, prost-build, and prost-types to 0.8.

* Update the last few places

examples/Cargo.toml

@@ -165,7 +165,7 @@ path = "src/mock/mock.rs"
 
 [dependencies]
 tonic = { path = "../tonic", features = ["tls"] }
-prost = "0.7"
+prost = "0.8"
 tokio = { version = "1.0", features = ["rt-multi-thread", "time", "fs", "macros", "net"] }
 tokio-stream = { version =  "0.1", features = ["net"] }
 async-stream = "0.3"
@@ -181,7 +181,7 @@ tracing-subscriber = { version = "0.2", features = ["tracing-log"] }
 tracing-attributes = "0.1"
 tracing-futures = "0.2"
 # Required for wellknown types
-prost-types = "0.7"
+prost-types = "0.8"
 # Hyper example
 hyper = "0.14"
 warp = "0.3"