Upgrade mux.js
Upgrade mux.js

Upgrade mux.js to verison 4.5.1 since it supports CEA608/708 closed
captions parsing for Dash now.

Issue: #1404.
Change-Id: I09c26dc44ba2e68734f201f58ba8856c836ed55e

shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player