Add missing LOCAL_MIN_SDK_VERSION for Support Library demos

Bug: 28302992
Change-Id: I456d407ba5442cd66571f307e02d5d26a4ee23aa
diff --git a/samples/SupportAppNavigation/Android.mk b/samples/SupportAppNavigation/Android.mk
index 6a30e1f..7d28ef0 100644
--- a/samples/SupportAppNavigation/Android.mk
+++ b/samples/SupportAppNavigation/Android.mk
@@ -11,6 +11,8 @@
 
 LOCAL_SDK_VERSION := current
 
+LOCAL_MIN_SDK_VERSION := 8
+
 include $(BUILD_PACKAGE)
 
 LOCAL_PROGUARD_FLAG_FILES := proguard.flags