Install the arm64 binary if we are on an arm64 macOS

[canova]

Hi @soulgalore!

Browsertime was failing to capture Firefox Profiler profiles with the "power" profiling feature enabled on my and @mrchrisadams's machines. After doing some debugging, I realized that it's because of the geckodriver binary we had. We are still using the x86_64 binary in arm64 machines and Marionette protocol was throwing some errors with this feature enabled. After switching to arm64 binary, I can confirm that the issue is fixed.

Here's a command to reproduce:

./bin/browsertime.js https://sitespeed.io -b firefox --firefox.geckoProfiler --firefox.geckoProfilerParams.features "power" -n 1

This was failing on arm64. I also tested on x84_64 macbooks and it doesn't fail there. When I manually update the sitespeedio/geckodriver dependency to use this branch, the issue gets fixed.

Also, this came up from the discussions in sitespeedio/sitespeed.io#3944

[soulgalore]

Thank you @canova !