Fix typo (#1710)

Fix typo in the CHANGELOG builder.

Author: martincostello

docs/_changelog/ChangeLogBuilder/MarkdownBuilder.cs

@@ -94,7 +94,7 @@ private async Task<string> Build()
             builder.AppendLine();
             builder.AppendLine($"In the [{milestone}]({milestoneHtmlUlr}) scope, ");
             builder.Append(issues.Count + " issues were resolved and ");
-            builder.AppendLine(pullRequests.Count + " pull requests where merged.");
+            builder.AppendLine(pullRequests.Count + " pull requests were merged.");
             builder.AppendLine($"This release includes {commits.Count} commits by {contributors.Count} contributors.");
             builder.AppendLine();
 
@@ -127,4 +127,4 @@ private void AppendList<T>(string title, IReadOnlyList<T> items, Func<T, string>
             builder.AppendLine();
         }
     }
-}
+}