Stop stderr noise from 'pip3 show typing'

Makefile

@@ -5,7 +5,7 @@ PY_SRC:=$(filter-out dmt/B_mappers/antlr.main.py dmt/A_mappers/Stubs.py, ${PY_SR
 # the one installed in $HOME/.local via setup.py.
 #
 # To address this, we find where our pip-installed typing lives:
-TYPING_FOLDER:=$(shell pip3 show typing | grep ^Location | sed 's,^.*: ,,')
+TYPING_FOLDER:=$(shell pip3 show typing 2>/dev/null | grep ^Location | sed 's,^.*: ,,')
 export PYTHONPATH=${TYPING_FOLDER}
 
 all:	flake8 pylint mypy coverage testDB