Add missing LOCAL_MIN_SDK_VERSION for Support Library demos

Bug: 28302992
Change-Id: I456d407ba5442cd66571f307e02d5d26a4ee23aa
diff --git a/samples/SupportPercentDemos/Android.mk b/samples/SupportPercentDemos/Android.mk
index 6395a84..164829f 100644
--- a/samples/SupportPercentDemos/Android.mk
+++ b/samples/SupportPercentDemos/Android.mk
@@ -21,6 +21,7 @@
 LOCAL_PACKAGE_NAME := SupportPercentDemos
 LOCAL_MODULE_TAGS := samples
 LOCAL_SDK_VERSION := current
+LOCAL_MIN_SDK_VERSION := 7
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 LOCAL_STATIC_JAVA_LIBRARIES := \
         android-support-percent \