printer: rejigger how we use serde_derive

The idea is that by bringing derives in via serde's optional feature, it
was inhibiting compilation speed[1]. We try to fix that by depending on
`serde_derive` as a distinct dependency.

It does seem to improve overall compilation time, but only by about 0.5
seconds. With that said, my machine has a lot of cores, so it's possible
this will help more on less powerful CPUs.

[1]: https://old.reddit.com/r/rust/comments/17rd8ww/faster_compilation_with_the_parallel_frontend_in/k8igjlg/

Cargo.lock

@@ -192,6 +192,7 @@ dependencies = [
  "grep-searcher",
  "log",
  "serde",
+ "serde_derive",
  "serde_json",
  "termcolor",
 ]
@@ -458,18 +459,18 @@ checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
 
 [[package]]
 name = "serde"
-version = "1.0.188"
+version = "1.0.193"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cf9e0fcba69a370eed61bcf2b728575f726b50b55cba78064753d708ddc7549e"
+checksum = "25dd9975e68d0cb5aa1120c288333fc98731bd1dd12f561e468ea4728c042b89"
 dependencies = [
  "serde_derive",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.188"
+version = "1.0.193"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4eca7ac642d82aa35b60049a6eccb4be6be75e599bd2e9adb5f875a737654af2"
+checksum = "43576ca501357b9b071ac53cdc7da8ef0cbd9493d8df094cd821777ea6e894d3"
 dependencies = [
  "proc-macro2",
  "quote",