implemented missing method on IObservableIssueCommentsClient

Octokit.Reactive/Clients/IObservableIssueCommentsClient.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
+using System.Reactive;
 
 namespace Octokit.Reactive
 {
@@ -57,5 +58,15 @@ namespace Octokit.Reactive
         /// <param name="commentUpdate">The modified comment</param>
         /// <returns></returns>
         IObservable<IssueComment> Update(string owner, string name, int number, string commentUpdate);
+
+        /// <summary>
+        /// Deletes the specified Issue Comment
+        /// </summary>
+        /// <remarks>http://developer.github.com/v3/issues/comments/#delete-a-comment</remarks>
+        /// <param name="owner">The owner of the repository</param>
+        /// <param name="name">The name of the repository</param>
+        /// <param name="number">The comment number</param>
+        /// <returns></returns>
+        IObservable<Unit> Delete(string owner, string name, int number);
     }
 }