Conversion fails for single file rules

[cdlm]

If you omit the source_dir or output_dir part in the regexp or in the result string, a directory with the name of the output file gets created. Guard then fails with a message like so:

14:40:20 - INFO - README.md >> README.html via template.erb
14:40:20 - ERROR - Guard::Markdown failed to achieve its <start>, exception was:
> [#34467539F48B] Errno::EISDIR: Is a directory - README.html
> [#34467539F48B] /Users/damien/.rbenv/versions/1.9.3-p429/lib/ruby/gems/1.9.1/gems/guard-markdown-0.2.0/lib/guard/markdown.rb:53:in `initialize'

[skuester]

I have also experienced this problem:

11:08:44 - INFO - Guard::Markdown has started watching your files
11:08:44 - INFO - README.md >> README.html
11:08:45 - ERROR - Guard::Markdown failed to achieve its <start>, exception was:
> [#C4C3A7370EC9] Errno::EISDIR: Is a directory - README.html
> [#C4C3A7370EC9] /Users/skuester/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/guard-markdown-0.2.0/lib/guard/markdown.rb:53:in `initialize'