Tweaked Bike Mount for Modular Mounting System

I took [yyh1002](https://www.thingiverse.com/yyh1002/about)'s [Customizable Bike Mount for Modular Mounting System](https://www.thingiverse.com/thing:2266715) and tweaked it a bit to suit my tastes. I added a fillet in the corner where the bracket's arms wrap the phone for strength, and a bulge at the tips of the arms to hold it even more securely (although this latter isn't particularly necessary; the original is secure enough as it is).

I also added some struts in the gap of the bracket so