Fix typo in runner selection in gulp

Author: weswigham

Diff for: scripts/build/tests.js

@@ -165,7 +165,7 @@ exports.cleanTestDirs = cleanTestDirs;
 function writeTestConfigFile(tests, runners, light, taskConfigsFolder, workerCount, stackTraceLimit, timeout, keepFailed) {
     const testConfigContents = JSON.stringify({
         test: tests ? [tests] : undefined,
-        runner: runners ? runners.split(",") : undefined,
+        runners: runners ? runners.split(",") : undefined,
         light,
         workerCount,
         stackTraceLimit,
@@ -192,4 +192,4 @@ function restoreSavedNodeEnv() {
 
 function deleteTemporaryProjectOutput() {
     return del(path.join(exports.localBaseline, "projectOutput/"));
-}
+}