Update polymer to version 0.5.4.
Update polymer to version 0.5.4.

Edit bower.json file to use latest version of polymer.

BUG=https://github.com/jackhou-chromium/bitmapper/issues/70
R=tapted@chromium.org

Review URL: https://codereview.appspot.com/199580043

jackhou-chromium/bitmapper,jackhou-chromium/bitmapper,jackhou-chromium/bitmapper