message: [now-cli] Only update build matches once per HTTP request
  Minor optimization since the "serve" function sometimes gets invoked
  recursively.
diff: @@ -651,6 +651,7 @@ export default class DevServer {
  if (config.version === 1) {
  this.output.error('Only `version: 2` is supported by `now dev`');
  await this.exit(1);
  + return;
  }
  await this.tryValidateOrExit(config, validateNowConfigBuilds);
  @@ -1251,7 +1252,9 @@ export default class DevServer {
  req.url = location;
  }
  + if (callLevel === 0) {
  await this.updateBuildMatches(nowConfig);
  + }
  if (this.blockingBuildsPromise) {
  debug('Waiting for builds to complete before handling request');
  