change user-modify command name to conform with the rest patterns

diff --git a/snf-astakos-app/astakos/im/management/commands/user-modify.py b/snf-astakos-app/astakos/im/management/commands/user-update.py
similarity index 100%
rename from snf-astakos-app/astakos/im/management/commands/user-modify.py
rename to snf-astakos-app/astakos/im/management/commands/user-update.py