clang: Fix security issues in update.sh script.
clang: Fix security issues in update.sh script.

- Use "${FOO}" for variable expansion.
- Use "$(CMD)" for command expansion.

Issues originally pointed in http://codereview.chromium.org/6588125/ by Markus.

BUG=None
TEST=run the script. It should works as before.

Review URL: http://codereview.chromium.org/6603002

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@76699 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser