update DR1 for tW for MG5 3.3.1

Dear all,

this is the fix to DR1 for tWX production in MG5 2.9.9 and 3.3.1. The way the amplitudes are added in the matrix_X.f files was changed. The new regex compensates for these changes.

The production was checked with tWZ and the total cross-section was compared with the old samples from https://its.cern.ch/jira/browse/ATLMCPROD-7290

Further tests for tW production are required @dhirsch @yanght

Kind regards,

Andrej