cache docker images.

Author: makasim

.travis.yml

@@ -32,9 +32,17 @@ matrix:
 cache:
     directories:
         - $HOME/.composer/cache
+        - $HOME/docker
+
+
+before_cache:
+    - >
+        mkdir -p $HOME/docker && docker images -a --filter='dangling=false' --format '{{.Repository}}:{{.Tag}} {{.ID}}'
+        | xargs -n 2 -t sh -c 'test -e $HOME/docker/$1.tar.gz || docker save $0 | gzip -2 > $HOME/docker/$1.tar.gz'
 
 before_install:
     - echo "extension = mongodb.so" >> $HOME/.phpenv/versions/$(phpenv version-name)/etc/php.ini
+    - if [[ -d $HOME/docker ]]; then ls $HOME/docker/*.tar.gz | xargs -I {file} sh -c "zcat {file} | docker load"; fi
 
 install:
     - rm $HOME/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini;