[OSX Fix] Update shebang and add OSX serial ports

nrfmon requires tcl8.6, but OSX Yosemite only provides 8.4 and/or 8.5. You can install tclsh8.6 (>=8.6.3) from ActiveState, but this installs to /usr/local/bin. This patch updates the shebang to use /bin/env in order to start tclsh8.6 from the correct place for OSX and Linux.

The second part of the patch adds OSX serial ports /dev/cu.usbmodem* to the port-enumerator so nrfmon can find them.

Note: Untested on linux