Undo breaking change to OptionsWrapper (#255)

Author: HaoK

src/Microsoft.Extensions.Options/OptionsWrapper.cs

@@ -22,9 +22,19 @@ public OptionsWrapper(TOptions options)
         /// </summary>
         public TOptions Value { get; }
 
+        public void Add(string name, TOptions options)
+        {
+            throw new NotImplementedException();
+        }
+
         public TOptions Get(string name)
         {
             return Value;
         }
+
+        public bool Remove(string name)
+        {
+            throw new NotImplementedException();
+        }
     }
 }