Pin the mdbook version for CI.

Fixes #779.

Author: emilio

ci/deploy-book.sh

@@ -4,7 +4,7 @@ set -xeu
 cd "$(dirname "$0")/../book"
 
 # Ensure mdbook is installed.
-cargo install mdbook || true
+cargo install mdbook --vers "^0.0.22" || true
 export PATH="$PATH:~/.cargo/bin"
 
 # Get the git revision we are on.

ci/test-book.sh

@@ -3,7 +3,7 @@
 set -xeu
 cd "$(dirname "$0")/../book"
 
-cargo install mdbook || true
+cargo install mdbook --vers "^0.0.22" || true
 export PATH="$PATH:~/.cargo/bin"
 
 mdbook build