use pip3 instead of pip because it's 2021 already

custompkg/root/etc/skel/Library/user-setup/100.install-python-packages.sh

@@ -7,5 +7,5 @@ PYTHON_PKGS="
 "
 
 for PKG in $PYTHON_PKGS ; do
-    /usr/local/bin/pip install --user $PKG
+    /usr/bin/pip3 install --user $PKG
 done