Set edition for process_wrapper and cargo_build_script_runner (#1254)

These otherwise get built with the downstream repo's default edition,
which is not necessarily correct.

Author: dtolnay

cargo/cargo_build_script_runner/BUILD.bazel

@@ -3,23 +3,27 @@ load("//rust:defs.bzl", "rust_binary", "rust_library", "rust_test")
 rust_library(
     name = "cargo_build_script_output_parser",
     srcs = ["lib.rs"],
+    edition = "2018",
 )
 
 rust_test(
     name = "test",
     crate = ":cargo_build_script_output_parser",
+    edition = "2018",
 )
 
 rust_binary(
     name = "cargo_build_script_runner",
     srcs = ["bin.rs"],
+    edition = "2018",
     visibility = ["//visibility:public"],
     deps = [":cargo_build_script_output_parser"],
 )
 
 rust_test(
     name = "bin_test",
     crate = ":cargo_build_script_runner",
+    edition = "2018",
     deps = [":cargo_build_script_runner"],
 )
 

util/process_wrapper/BUILD.bazel

@@ -6,12 +6,14 @@ load("//rust/private:rust.bzl", "rust_binary_without_process_wrapper")
 rust_binary_without_process_wrapper(
     name = "process_wrapper",
     srcs = glob(["*.rs"]),
+    edition = "2018",
     visibility = ["//visibility:public"],
 )
 
 rust_test(
     name = "process_wrapper_test",
     crate = ":process_wrapper",
+    edition = "2018",
 )
 
 filegroup(