rustdoc: update pulldown renderer

fixes rust-lang#45420

Author: QuietMisdreavus

src/Cargo.lock

@@ -13,7 +13,7 @@ doctest = false
 [dependencies]
 env_logger = { version = "0.4", default-features = false }
 log = "0.3"
-pulldown-cmark = { version = "0.0.14", default-features = false }
+pulldown-cmark = { version = "0.1.0", default-features = false }
 html-diff = "0.0.4"
 
 [build-dependencies]