Add missing backlash in run-windows-k8s-migration.sh

Author: mauriciopoppe

test/run-windows-k8s-migration.sh

@@ -57,7 +57,7 @@ base_cmd="${PKGDIR}/bin/k8s-integration-test \
     --deploy-overlay-name=${overlay_name} \
     --test-version=${test_version} \
     --kube-version=${kube_version} \
-    --kube-feature-gates=${feature_gates}
+    --kube-feature-gates=${feature_gates} \
     --storageclass-files=sc-windows.yaml \
     --snapshotclass-file=pd-volumesnapshotclass.yaml \
     --test-focus=${GCE_PD_TEST_FOCUS} \