Check rustfmt formatting in travis builds (#210)

* Install rustfmt

* Check formatting in travis builds

.travis.yml

@@ -5,6 +5,8 @@ rust:
     
 cache: cargo
 
+before_script: (cargo install rustfmt || true)
+
 sudo: false
 
 notifications:

scripts/travis-build.sh

@@ -5,6 +5,10 @@ set -e
 # build rust project
 make
 
+# check formatting (rustfmt)
+PATH=~/.cargo/bin:$PATH
+cargo fmt -- --write-mode=diff
+
 # clone hugo branch, which contains the blog template
 git clone --branch=hugo https://github.com/phil-opp/blog_os.git hugo
 cd hugo