Change pkg/stack_trace's version to 0.9.3.

Apparently I screwed up the versioning earlier and went from 0.9.2 to 0.9.2-dev
instead of 0.9.3-dev.

R=rnystrom@google.com
BUG=

Review URL: https://codereview.chromium.org//206833004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/stack_trace@34214 260f80e4-7a28-3924-810f-c04153c831b5