Update mdbook.

Author: ehuss

Cargo.lock

@@ -1495,9 +1495,9 @@ dependencies = [
 
 [[package]]
 name = "handlebars"
-version = "3.4.0"
+version = "4.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5deefd4816fb852b1ff3cb48f6c41da67be2d0e1d20b26a7a3b076da11f064b1"
+checksum = "72a0ffab8c36d0436114310c7e10b59b3307e650ddfabf6d006028e29a70c6e6"
 dependencies = [
  "log",
  "pest",
@@ -2100,9 +2100,9 @@ dependencies = [
 
 [[package]]
 name = "mdbook"
-version = "0.4.7"
+version = "0.4.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "28f6a882f3880ec68e96f60d6b543c34941e2f307ad10e2992e4db9acfe96529"
+checksum = "4ee73932975c44c485e541416d7c30abb31a053af7e49682f6e856f1e4d6ab2a"
 dependencies = [
  "ammonia",
  "anyhow",

src/tools/rustbook/Cargo.toml

@@ -10,6 +10,6 @@ clap = "2.25.0"
 env_logger = "0.7.1"
 
 [dependencies.mdbook]
-version = "0.4.6"
+version = "0.4.11"
 default-features = false
 features = ["search"]