[WIP] Test properly, when multiple cookbooks are modified.

When multiple cookbooks are modified,
the current task does not test any one of the cookbooks,
because of the argument of the `split` function.

When specifying line-space, the argument should be surrounded by " now '.
Test properly, when multiple cookbooks are modified.

When multiple cookbooks are modified,
the current task does not test any one of the cookbooks,
because of the argument of the `split` function.

When specifying line-space, the argument should be surrounded by " not '.

```
diff --git a/tasks/tests/ci.rake b/tasks/tests/ci.rake
index 931d7e7..5f69eda 100755
--- a/tasks/tests/ci.rake
+++ b/tasks/tests/ci.rake
@@ -6,7 +6,7 @@ desc "Run CI tests."
 task :test do
   cookbooks = `git diff --name-only master..$(git symbolic-ref HEAD) | grep site-cookbooks | cut -f 2 -d / | awk '!a[$0]++'`

-  cookbooks.split('\n').each do |cookbook|
+  cookbooks.split("\n").each do |cookbook|
     cookbook.strip!

     cd "site-cookbooks/#{cookbook}/" do
```
Merge pull request #161 from kazu634/hotfix-for-test-task

Test properly, when multiple cookbooks are modified.