docs: Fix docs.rs builds

We were broken by rust-lang/cargo#10343.

See rust-lang/cargo#11425

Fixes #4519

Author: epage

Cargo.toml

@@ -37,7 +37,7 @@ include = [
 [package.metadata.docs.rs]
 features = ["unstable-doc"]
 rustdoc-args = ["--cfg", "docsrs"]
-cargo-args = ["-Zunstable-options", "-Zrustdoc-scrape-examples=examples"]
+cargo-args = ["-Zunstable-options", "-Zrustdoc-scrape-examples"]
 
 [package.metadata.playground]
 features = ["unstable-doc"]