Add the arithmetic transformer endpoint to setup.cfg

The arithmetic transformer patch at
I1b637e5b1d1bb15ed3c3d7ec758d2a684eaccf21 did not
add the new transformer into the setup.cfg's endpoints, so
this patch does.

Change-Id: I465dc34067915297e19bbb1718c8911e579a3112
Merge "Add the arithmetic transformer endpoint to setup.cfg"