feat: Update prost and friends to 0.9 (#791)

tonic-build/Cargo.toml

@@ -1,10 +1,10 @@
 [package]
 name = "tonic-build"
-version = "0.5.2"
+version = "0.6.0"
 authors = ["Lucio Franco <[email protected]>"]
 edition = "2018"
 license = "MIT"
-documentation = "https://docs.rs/tonic-build/0.5.2/tonic_build/"
+documentation = "https://docs.rs/tonic-build/0.6.0/tonic_build/"
 repository = "https://github.com/hyperium/tonic"
 homepage = "https://github.com/hyperium/tonic"
 description = """
@@ -16,7 +16,7 @@ keywords = ["rpc", "grpc", "async", "codegen", "protobuf"]
 
 
 [dependencies]
-prost-build = { version = "0.8", optional = true }
+prost-build = { version = "0.9", optional = true }
 syn = "1.0"
 quote = "1.0"
 proc-macro2 = "1.0"