Directly launch studio task on the root project

There is only one studio task and it is on the root project.
Launch this task directly via :studio which avoid configuring
all the other projects.

Test: ./studiow all -> now takes <1s (was ~10s)
Change-Id: I1d7988db4b59ed20188e8926b755d97ce75daebe

diff --git a/studiow b/studiow
index 485d33d..e0110f9 100755
--- a/studiow
+++ b/studiow

@@ -120,5 +120,5 @@
   ./cleanBuild.sh -y studio
 else
   # ask gradle to launch studio
-  ./gradlew studio
+  ./gradlew :studio
 fi