Make @stream initialCount NonNull (#4322)

Updated to reflect spec draft
graphql/graphql-spec#1132

Also changed the argument order to match the spec draft

src/type/directives.ts

@@ -204,6 +204,11 @@ export const GraphQLStreamDirective = new GraphQLDirective({
     'Directs the executor to stream plural fields when the `if` argument is true or undefined.',
   locations: [DirectiveLocation.FIELD],
   args: {
+    initialCount: {
+      default: { value: 0 },
+      type: new GraphQLNonNull(GraphQLInt),
+      description: 'Number of items to return immediately',
+    },
     if: {
       type: new GraphQLNonNull(GraphQLBoolean),
       description: 'Stream when true or undefined.',
@@ -213,11 +218,6 @@ export const GraphQLStreamDirective = new GraphQLDirective({
       type: GraphQLString,
       description: 'Unique name',
     },
-    initialCount: {
-      default: { value: 0 },
-      type: GraphQLInt,
-      description: 'Number of items to return immediately',
-    },
   },
 });