Exclude build-version file from status output

The git-status-check verifies .gitignore files depends on no
extraneous files being created. traf-functions was already changed
to avoid/hide files that it creates, but the file created in this
file was missed.

This causes the build-check job fail.

Change-Id: I2e534c61a657d2c68a0f2b8dd542e176104bddbb