use older mdbook

.travis.yml

@@ -79,7 +79,7 @@ after_success:
     if [[ "$TRAVIS_OS_NAME" == "linux" && "$TRAVIS_PULL_REQUEST" = "false" && "$TRAVIS_BRANCH" == "master" && "$TRAVIS_RUST_VERSION" == "beta" ]]; then
       cargo doc --features "alpn, tls, session" --no-deps &&
       echo "<meta http-equiv=refresh content=0;url=os_balloon/index.html>" > target/doc/index.html &&
-      curl -sL https://github.com/rust-lang-nursery/mdBook/releases/download/v0.1.5/mdbook-v0.1.5-x86_64-unknown-linux-gnu.tar.gz | tar xvz -C $HOME/.cargo/bin &&
+      curl -sL https://github.com/rust-lang-nursery/mdBook/releases/download/v0.1.3/mdbook-v0.1.3-x86_64-unknown-linux-gnu.tar.gz | tar xvz -C $HOME/.cargo/bin &&
       cd guide && mdbook build -d ../target/doc/guide && cd .. &&
       git clone https://github.com/davisp/ghp-import.git &&
       ./ghp-import/ghp_import.py -n -p -f -m "Documentation upload" -r https://"$GH_TOKEN"@github.com/"$TRAVIS_REPO_SLUG.git" target/doc &&

CHANGES.md

@@ -1,6 +1,12 @@
 # Changes
 
-## 0.5.0
+
+## 0.5.1 (2018-xx-xx)
+
+* Client connector provides stats, `ClientConnector::stats()`
+
+
+## 0.5.0 (2018-04-10)
 
 * Type-safe path/query/form parameter handling, using serde #70