fix(reset): catch grep failure so script doesn't die

with -e, the script returns an error code whenever any command does so,
which can cause the rest of the Dev Container setup to fail

grep returns an error code when no match is found, but we don't want
that to end the script in error, so test the grep return code

see https://stackoverflow.com/a/49627999/453168

bin/reset_db.sh

@@ -23,7 +23,7 @@ else
     echo "DB_RESET is false, skipping"
 fi
 
-valid_fixtures=$(echo "$DJANGO_DB_FIXTURES" | grep -e fixtures\.json$)
+valid_fixtures=$(echo "$DJANGO_DB_FIXTURES" | grep -e fixtures\.json$ || test $? = 1)
 
 if [[ -n "$valid_fixtures" ]]; then
     # load data fixtures