Rename godog.Feature alias to godog.GherkinDocument to be more accurate (#422)

test_context.go

@@ -13,8 +13,8 @@ import (
 	"github.com/cucumber/godog/internal/models"
 )
 
-// Feature represents gherkin document.
+// GherkinDocument represents gherkin document.
-type Feature = messages.GherkinDocument
+type GherkinDocument = messages.GherkinDocument
 
 // Scenario represents the executed scenario
 type Scenario = messages.Pickle