Cache cargo

.travis.yml

@@ -24,4 +24,8 @@ after_success: |
   echo "<meta http-equiv=refresh content=0;url=`echo $TRAVIS_REPO_SLUG | cut -d '/' -f 2`/index.html>" > target/doc/index.html &&
   sudo pip install ghp-import &&
   ghp-import -n target/doc &&
-  git push -fq https://${GH_TOKEN}@github.com/${TRAVIS_REPO_SLUG}.git gh-pages
+  git push -fq https://${GH_TOKEN}@github.com/${TRAVIS_REPO_SLUG}.git gh-pages
+cache: cargo
+before_cache:
+  # Travis can't cache files that are not readable by "others"
+  - chmod -R a+r $HOME/.cargo