Update some deps to cut down on rebuilds (#1551)

This updates a few dependencies to avoid rebuilding extraneously when
possible on CI. While this doesn't fix everything it should at least be
part of the solution!

Cargo.lock

@@ -50,9 +50,9 @@ checksum = "d9a60d744a80c30fcb657dfe2c1b22bcb3e814c1a1e3674f32bf5820b570fbff"
 
 [[package]]
 name = "arbitrary"
-version = "0.4.1"
+version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "75153c95fdedd7db9732dfbfc3702324a1627eec91ba56e37cd0ac78314ab2ed"
+checksum = "1148c9b25d393a07c4cc3ef5dd30f82a40a1c261018c4a670611ed8e76cad3ea"
 dependencies = [
  "derive_arbitrary",
 ]
@@ -639,13 +639,13 @@ dependencies = [
 
 [[package]]
 name = "derive_arbitrary"
-version = "0.4.0"
+version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "caedd6a71b6d00bdc458ec8ffbfd12689c1ee7ffa69ad9933310aaf2f08f18d8"
+checksum = "9735d3bee627701429c04d0e5bbaa966d22dcd64e50e4296e5aa960a15159881"
 dependencies = [
  "proc-macro2",
+ "quote",
  "syn",
- "synstructure",
 ]
 
 [[package]]
@@ -1603,9 +1603,9 @@ dependencies = [
 
 [[package]]
 name = "regex"
-version = "1.3.6"
+version = "1.3.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f6946991529684867e47d86474e3a6d0c0ab9b82d5821e314b1ede31fa3a4b3"
+checksum = "a6020f034922e3194c711b82a627453881bc4682166cabb07134a10c26ba7692"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -1864,18 +1864,6 @@ dependencies = [
  "syn",
 ]
 
-[[package]]
-name = "synstructure"
-version = "0.12.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "67656ea1dc1b41b1451851562ea232ec2e5a80242139f7e679ceccfb5d61f545"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn",
- "unicode-xid",
-]
-
 [[package]]
 name = "target-lexicon"
 version = "0.10.0"