rspec tests doesn't work on windows

I can run rspec tests with success on linux.
But that doesn't work on windows.
It seems that rspec doesn't detect test examples.

Here is the result when I execute `bundle exec rspec` with `logstash-filter-multiline` plugin on windows :

```
No examples found.

Finished in 0 seconds
0 examples, 0 failures
```

My environment :
- windows 7 - 64 bits
- java 7
- logstash 1.5.rc4

Reproduce `bundle exec rspec` on Windows with the `logstash-filter-multiline` plugin and compare it with Linux, using the reported Windows 7, Java 7, and Logstash 1.5.rc4 environment. Trace why RSpec reports no examples; done means the plugin's tests are discovered and execute on Windows rather than reporting zero examples.

Written by the indexing model from the issue text.