Autocargo-ed serde_php (#80)

Summary:
Pull Request resolved: #80

Trying to use this in `ctp` codebase, where most things are autocargo compatible.
Looks like it can be auto-cargoed as it doesn't have any fancy deps.

So I followed the instructions here to make that happen:
https://www.internalfb.com/intern/wiki/Rust-at-facebook/Cargo.toml_from_Buck_(autocargo)/

Reviewed By: farnz

Differential Revision: D27079404

fbshipit-source-id: 83c10c2899a6a0da52c8f3379c9fbfcde5052eea

Author: iammxt

eden/mononoke/walker/Cargo.toml

@@ -43,7 +43,7 @@ fsnodes = { version = "0.1.0", path = "../derived_data/fsnodes" }
 futures = { version = "0.3.13", features = ["async-await", "compat"] }
 hash_memo = { version = "0.1.0", git = "https://github.com/facebookexperimental/rust-shed.git", branch = "master" }
 hex = "0.4"
-internment = { version = "0.4.1", features = ["serde"] }
+internment = { version = "0.4.2", features = ["serde"] }
 itertools = "0.8"
 manifest = { version = "0.1.0", path = "../manifest" }
 maplit = "1.0"