fix Cargo.toml

Author: RalfJung

Cargo.toml

@@ -33,6 +33,8 @@ required-features = ["rustc_tests"]
 cargo_metadata = { version = "0.9.0", optional = true }
 directories = { version = "2.0", optional = true }
 rustc_version = { version = "0.2.3", optional = true }
+serde_json = { version = "1.0.44", optional = true }
+
 getrandom = { version = "0.1.8", features = ["std"] }
 byteorder = "1.3"
 env_logger = "0.7.1"
@@ -50,14 +52,13 @@ rustc-workspace-hack = "1.0.0"
 # between "cargo build" and "cargo intall".
 num-traits = "*"
 serde = { version = "*", features = ["derive"] }
-serde_json = "1.0.44"
 
 [build-dependencies]
 vergen = "3"
 
 [features]
 default = ["cargo_miri"]
-cargo_miri = ["cargo_metadata", "directories", "rustc_version"]
+cargo_miri = ["cargo_metadata", "directories", "rustc_version", "serde_json"]
 rustc_tests = []
 
 [dev-dependencies]