Fixed warning in DiffService.cs.

Author: Myoxocephalus

src/GitHub.InlineReviews/Services/DiffService.cs

@@ -39,7 +39,7 @@ public async Task<IReadOnlyList<DiffChunk>> Diff(
             }
             else
             {
-                return new DiffChunk[0];
+                return Array.Empty<DiffChunk>();
             }
         }
 
@@ -59,7 +59,7 @@ public async Task<IReadOnlyList<DiffChunk>> Diff(
             }
             else
             {
-                return new DiffChunk[0];
+                return Array.Empty<DiffChunk>();
             }
         }
     }