Merge pull request #3989 from rust-lang/renovate/mdbook-0.x

Update dependency mdbook to v0.5.4

Author: ehuss

.github/workflows/deploy.yml

@@ -6,7 +6,7 @@ on:
 
 env:
   # renovate: datasource=crate depName=mdbook versioning=semver
-  MDBOOK_VERSION: 0.5.3
+  MDBOOK_VERSION: 0.5.4
 
 jobs:
   build: