Fix newvers.sh on macOS 10.15

[arichardson]

Summary

It appears that the /bin/sh echo now defaults to -e and therefore the
#define VERSTR included newline characters instead of \n which caused
compiler errors.
A less fragile solution might be to bootstrap the in-tree /bin/sh but that
requires more changes.

Test Plan

VERSTR contained a newline before, now contains \n