Handle incomplete examples to scenario outlines. Fixes cucumber#109.

Gherkin v4.0 is more allowing with respect to incomplete scenario
outlines, therefore Cucumber::Core::Gherkin::AstBuilder need to also be
that.

HISTORY.md

@@ -7,6 +7,7 @@
 
 ### Bugfixes
 
+* Handle incomplete examples to scenario outlines. ([109](https://github.com/cucumber/cucumber-ruby-core/pull/109) @brasmusson)
 * Add with_filtered_backtrace method to unknown result ([107](https://github.com/cucumber/cucumber-ruby-core/pull/107) @dansscheider)
 
 ## [v1.5.0](https://github.com/cucumber/cucumber-ruby-core/compare/v1.4.0...v1.5.0)