Handle ReadFormAsync breaking change.

src/Microsoft.AspNet.Diagnostics.Elm/ElmPageMiddleware.cs

@@ -93,7 +93,7 @@ namespace Microsoft.AspNet.Diagnostics.Elm
                 NamePrefix = string.Empty
             };
             var isRedirect = false;
-            var form = await context.Request.GetFormAsync();
+            var form = await context.Request.ReadFormAsync();
             if (form.ContainsKey("clear"))
             {
                 _store.Clear();

src/Microsoft.AspNet.Diagnostics.Entity/MigrationsEndPointMiddleware.cs

@@ -78,7 +78,7 @@ namespace Microsoft.AspNet.Diagnostics.Entity
 
         private static async Task<DbContext> GetDbContext(HttpContext context, ILogger logger)
         {
-            var form = await context.Request.GetFormAsync().WithCurrentCulture();
+            var form = await context.Request.ReadFormAsync().WithCurrentCulture();
             var contextTypeName = form["context"];
             if (string.IsNullOrWhiteSpace(contextTypeName))
             {