Cache only apt and ruby from vendor

Since introduction of gitignore the vendor folder contains also gitignores which affects detection when to update a cache.
We explicitly cache only apt and ruby folders.

.gitlab-ci.yml

@@ -7,7 +7,8 @@ services:
 cache:
   key: "ruby21"
   paths:
-  - vendor
+  - vendor/apt
+  - vendor/ruby
 variables:
   MYSQL_ALLOW_EMPTY_PASSWORD: "1"

scripts/prepare_build.sh

@@ -16,10 +16,10 @@ retry() {
 }
 if [ -f /.dockerenv ] || [ -f ./dockerinit ]; then
-    mkdir -p vendor
+    mkdir -p vendor/apt
     # Install phantomjs package
-    pushd vendor
+    pushd vendor/apt
     if [ ! -e phantomjs_1.9.8-0jessie_amd64.deb ]; then
         wget -q https://gitlab.com/axil/phantomjs-debian/raw/master/phantomjs_1.9.8-0jessie_amd64.deb
     fi