Combine rustdoc semver exempt cfg into one argument

Author: dtolnay

Cargo.toml

@@ -13,8 +13,8 @@ repository = "https://github.com/dtolnay/proc-macro2"
 rust-version = "1.56"
 
 [package.metadata.docs.rs]
-rustc-args = ["--cfg", "procmacro2_semver_exempt"]
-rustdoc-args = ["--cfg", "procmacro2_semver_exempt", "--generate-link-to-definition"]
+rustc-args = ["--cfg=procmacro2_semver_exempt"]
+rustdoc-args = ["--cfg=procmacro2_semver_exempt", "--generate-link-to-definition"]
 targets = ["x86_64-unknown-linux-gnu"]
 
 [package.metadata.playground]