Build calendar-common against SDK 15.

Change-Id: Ia004f7bf624e9a940c0f596df558cc7f3e0d1b51
diff --git a/Android.mk b/Android.mk
index f885174..99aca7f 100644
--- a/Android.mk
+++ b/Android.mk
@@ -16,7 +16,7 @@
 
 include $(CLEAR_VARS)
 LOCAL_MODULE := calendar-common
-LOCAL_SDK_VERSION := current
+LOCAL_SDK_VERSION := 15
 LOCAL_SRC_FILES := \
     $(call all-java-files-under, src) \
     $(call all-java-files-under, ../../../external/libphonenumber/java/src)