[proc-macro-nested] Expose proc-macro-nested

This crate is necessary when importing a recursive proc_macro.

Change-Id: I81adff72ebaff5650620f712aa241768d6be7fce
diff --git a/rustc_deps/Cargo.lock b/rustc_deps/Cargo.lock
index deb1904..1ac7942 100644
--- a/rustc_deps/Cargo.lock
+++ b/rustc_deps/Cargo.lock
@@ -530,6 +530,7 @@
  "pin-utils 0.1.0-alpha.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "pretty_assertions 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "proc-macro-hack 0.5.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro-nested 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "proc-macro2 0.4.24 (registry+https://github.com/rust-lang/crates.io-index)",
  "proptest 0.8.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "quote 0.6.10 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/rustc_deps/Cargo.toml b/rustc_deps/Cargo.toml
index eff48cc..3ec012f 100644
--- a/rustc_deps/Cargo.toml
+++ b/rustc_deps/Cargo.toml
@@ -51,6 +51,7 @@
 pin-utils = "=0.1.0-alpha.4"
 pretty_assertions = "0.5.1"
 proc-macro-hack = "0.5.4"
+proc-macro-nested = "0.1.2"
 proptest = "0.8.7"
 rand = "0.6"
 rand_core = "0.4.0"