Tweak spec
Tweak spec

When bundler pre version is released, spec is failed

https://travis-ci.org/sue445/sengiri_yaml/jobs/273232578

```
  1) SengiriYaml sengiri_yaml without 2 args should eq "sengiri_yaml <source_yaml> <destination_dir>\n"
     Failure/Error: it{ should eq help }

       expected: "sengiri_yaml <source_yaml> <destination_dir>\n"
            got: "sengiri_yaml <source_yaml> <destination_dir>\nThe latest bundler is 1.16.0.pre.2, but you are currently running 1.15.1.\nTo update, run `gem install bundler --pre`\n"

       (compared using ==)

       Diff:
       @@ -1,2 +1,4 @@
        sengiri_yaml <source_yaml> <destination_dir>
       +The latest bundler is 1.16.0.pre.2, but you are currently running 1.15.1.
       +To update, run `gem install bundler --pre`
```

Close #6

sue445/sengiri_yaml