docs: included dart_package.md missing "coverage" URL (#160)

Author: alestiago

site/docs/workflows/dart_package.md

@@ -68,7 +68,7 @@ The Dart package workflow consists of the following steps:
 
 ### `check_ignore`
 
-**Optional** Allows ignoring lines from [coverage][coverage].
+**Optional** Allows ignoring lines from [coverage](https://pub.dev/packages/coverage).
 
 **Default** `false`