ADT 20.0.0 => 21.0.0 dev

Change-Id: Idde24b6b893d1029d48ba32766110a6a3cdf73c6
diff --git a/files/tools_source.properties b/files/tools_source.properties
index d17ac45..3876b3f 100644
--- a/files/tools_source.properties
+++ b/files/tools_source.properties
@@ -1,3 +1,3 @@
 Pkg.UserSrc=false
-Pkg.Revision=20
+Pkg.Revision=21
 Platform.MinPlatformToolsRev=12