fix: Fix compilation error with strict constness

The MediaCapabilities polyfill caused compiler errors in stricter
environments, in which navigator.mediaCapabilities was marked as
const.  This suppresses constness errors from the compiler in the
install method of the polyfill.

Change-Id: Idb47a473335c886a2a7b3c77b84ce8f51fce4114

lib/polyfill/media_capabilities.js

@@ -19,6 +19,7 @@ goog.require('shaka.util.Platform');
 shaka.polyfill.MediaCapabilities = class {
   /**
    * Install the polyfill if needed.
+   * @suppress {const}
    */
   static install() {
     shaka.log.debug('MediaCapabilities: install');