Update tools/pip-requires for prettytable

changes pip-requires from:
    prettytable>=0.6,<0.7
to:
    prettytable>=0.6,<0.8

Change-Id: Ic04d38078ad06e43947b5e98b26576a4c51dbbb0
Authored-by: Chris Krelle <nobodycam@gmail.com>
Merge "Update tools/pip-requires for prettytable"