Bump synstructure 0.12.5 -> 0.12.6

Summary:
Automated semver-compatible version bump.
bypass-github-export-checks

Reviewed By: dtolnay

Differential Revision: D94686364

fbshipit-source-id: 1ea799019fa0ef739c0988f92ab1f90a9624fcb6

Author: generatedunixname2066905484085733

hphp/hack/src/Cargo.lock

@@ -20,4 +20,4 @@ proc-macro2 = { version = "1.0.106", features = ["span-locations"] }
 quote = "1.0.44"
 signed_source = { version = "0.0.0", path = "../utils/rust/signed_source" }
 syn = { version = "1.0.109", features = ["extra-traits", "fold", "full", "visit", "visit-mut"] }
-synstructure = "0.12"
+synstructure = "0.12.6"

hphp/hack/src/hh_codegen/Cargo.toml

@@ -17,4 +17,4 @@ edition = "2018"
 [dependencies]
 proc-macro2 = { version = "1.0.106", features = ["span-locations"] }
 quote = "1.0.44"
-synstructure = "0.12"
+synstructure = "0.12.6"

hphp/hack/src/utils/eq_modulo_pos_derive/Cargo.toml

@@ -18,4 +18,4 @@ edition = "2018"
 proc-macro2 = { version = "1.0.106", features = ["span-locations"] }
 quote = "1.0.44"
 syn = { version = "1.0.109", features = ["extra-traits", "fold", "full", "visit", "visit-mut"] }
-synstructure = "0.12"
+synstructure = "0.12.6"