Fix schema filename

Author: essaji

packages/apollo/src/commands/client/download-schema.ts

@@ -19,9 +19,7 @@ export default class SchemaDownload extends ClientCommand {
   static args = [
     {
       name: "output",
-      description: "Path to write the introspection result to",
-      required: true,
-      default: "schema.json"
+      description: "Path to write the introspection result to"
     }
   ];
 
@@ -30,7 +28,9 @@ export default class SchemaDownload extends ClientCommand {
     let gitContext;
     await this.runTasks(({ args, project, flags }) => {
       const isSDLFormat = flags.target && flags.target.toUpperCase() === "SDL";
-      const output = isSDLFormat ? "schema.graphql" : args.output;
+      console.log(args);
+      const output =
+        args.output || (isSDLFormat ? "schema.graphql" : "schema.json");
       return [
         {
           title: `Saving schema to ${output}`,