LUX update: lux.js v216

We have released v216 of lux.js. This release contains bug fixes and other improvements:

• Long tasks buffering (which was previously reverted in v214) has been reinstated, enabling LUX to instrument long tasks that occurred before the snippet.
• JavaScript page labels are now evaluated quicker than before.
• LUX can now use a simpler beacon mechanism with LUX.beaconMode = "simple". This sends a beacon by inserting an image into the page, rather than a <script> tag.