Replace try-finally by using.

Rx.NET/Source/src/System.Reactive/Linq/Observable/SelectMany.cs

@@ -392,7 +392,7 @@ namespace System.Reactive.Linq.ObservableImpl
                         return;
                     }
 
-                    try
+                    using (e)
                     {
                         var hasNext = true;
 
@@ -420,10 +420,6 @@ namespace System.Reactive.Linq.ObservableImpl
                             }
                         }
                     }
-                    finally
-                    {
-                        e.Dispose();
-                    }
                 }
             }
         }
@@ -485,7 +481,7 @@ namespace System.Reactive.Linq.ObservableImpl
                         return;
                     }
 
-                    try
+                    using (e)
                     {
                         var eIndex = 0;
                         var hasNext = true;
@@ -514,10 +510,6 @@ namespace System.Reactive.Linq.ObservableImpl
                             }
                         }
                     }
-                    finally
-                    {
-                        e.Dispose();
-                    }
                 }
             }
         }
@@ -1361,7 +1353,7 @@ namespace System.Reactive.Linq.ObservableImpl
                         return;
                     }
 
-                    try
+                    using (e)
                     {
                         var hasNext = true;
 
@@ -1389,10 +1381,6 @@ namespace System.Reactive.Linq.ObservableImpl
                             }
                         }
                     }
-                    finally
-                    {
-                        e.Dispose();
-                    }
                 }
             }
         }
@@ -1448,7 +1436,7 @@ namespace System.Reactive.Linq.ObservableImpl
                         return;
                     }
 
-                    try
+                    using (e)
                     {
                         var hasNext = true;
 
@@ -1476,10 +1464,6 @@ namespace System.Reactive.Linq.ObservableImpl
                             }
                         }
                     }
-                    finally
-                    {
-                        e.Dispose();
-                    }
                 }
             }
         }