Update PRODUCT_SHIPPING_API_LEVEL for gs101 devices

Test: adb shell getprop ro.product.first_api_level
Bug: 202921268
Change-Id: I3de89e705c1e7f0bac5f6d4b4b2791ef2edcfec6
Signed-off-by: Alex Hong <rurumihong@google.com>
diff --git a/device-slider.mk b/device-slider.mk
index 47f85ea..acfcf4c 100644
--- a/device-slider.mk
+++ b/device-slider.mk
@@ -109,3 +109,6 @@
 # Bluetooth HAL
 PRODUCT_PACKAGES += \
 	bt_vendor.conf
+
+# This device is shipped with 31 (Android S)
+PRODUCT_SHIPPING_API_LEVEL := 31