Tools 21 depends on Platform-Tools 15 rc9.

Change-Id: Ia853e7d6e220d518a24cc83f53eb55d84b7b1c24
diff --git a/files/tools_source.properties b/files/tools_source.properties
index b8ba4f7..c62f80d 100644
--- a/files/tools_source.properties
+++ b/files/tools_source.properties
@@ -1,3 +1,3 @@
 Pkg.UserSrc=false
 Pkg.Revision=21
-Platform.MinPlatformToolsRev=15 rc5
+Platform.MinPlatformToolsRev=15 rc9