powerbank-bike-clamp: hinge side lobes

powerbank-bike-clamp: hinge side lobes

Previous print broke at the "inner" "body".  This leads me to theorise
that inner lobes are more vulnerable.  Maybe doing this will arrange
that any future break is in the clamp (which is smaller to print).

Also more lobes mahy spread the load more.  The key edge is now at
79.5% rather than 74.3% of the distance across.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>