envsetup: Mark zsh as compatible

Basic functionality has been tested on zsh 5.0.2 and has been found to
work correctly.

Change-Id: I02e5e3bedf56b43104c280d9737ae7b334357643
diff --git a/envsetup.sh b/envsetup.sh
index cf61950..084d5cf 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -1642,8 +1642,10 @@
     case `ps -o command -p $$` in
         *bash*)
             ;;
+        *zsh*)
+            ;;
         *)
-            echo "WARNING: Only bash is supported, use of other shell would lead to erroneous results"
+            echo "WARNING: Only bash and zsh are supported, use of other shell may lead to erroneous results"
             ;;
     esac
 fi