add droiddoc flag to include since-tags for api level 8

Change-Id: Ib7dc5114b075001cdf78db96dbbaa99644836f8b
diff --git a/Android.mk b/Android.mk
index 10b6d67..8783934 100644
--- a/Android.mk
+++ b/Android.mk
@@ -369,6 +369,7 @@
     -since ./frameworks/base/api/5.xml 5 \
     -since ./frameworks/base/api/6.xml 6 \
     -since ./frameworks/base/api/7.xml 7 \
+    -since ./frameworks/base/api/8.xml 8 \
 		-error 1 -error 2 -warning 3 -error 4 -error 6 -error 8 \
 		-overview $(LOCAL_PATH)/core/java/overview.html