Add ramdisk.img to the dist dir.

Change-Id: Ia74c501298010734dd1b8db8df86720d3e8bb7cd
http://b/issue?id=2590492
diff --git a/core/main.mk b/core/main.mk
index f830f03..71e8acb 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -702,6 +702,7 @@
 	$(INSTALLED_BUILD_PROP_TARGET) \
 	$(BUILT_TARGET_FILES_PACKAGE) \
 	$(INSTALLED_ANDROID_INFO_TXT_TARGET) \
+	$(INSTALLED_RAMDISK_TARGET) \
  )
 
 # Tests are installed in userdata.img.  If we're building the tests