Closes #9

### Fixes

- #9 : `gsub!` changed to `gsub` to prevent `nil` value if match fails. 
 [Here](https://github.com/allure-framework/allure-cucumber/blob/master/lib/allure-cucumber/formatter.rb#L18) if feature name was in single line then feature name was set as "" , causing non-unique suite_names for the the xml report. 

cc: @smecsia