Fix conflicting short flag -u when executing migrate generate command

[billy1624]

Fixes

• Fix conflicting short flag -u when executing migrate generate command

Before the fix:

➜ sea-orm-cli migrate generate -h
sea-orm-cli-migrate-generate
Generate a new, empty migration

USAGE:
    sea-orm-cli migrate generate [OPTIONS] <MIGRATION_NAME>

ARGS:
    <MIGRATION_NAME>    Name of the new migration

OPTIONS:
    -d, --migration-dir <MIGRATION_DIR>
            Migration script directory.
            If your migrations are in their own crate,
            you can provide the root of that crate.
            If your migrations are in a submodule of your app,
            you should provide the directory of that submodule. [default: ./migration]

    -h, --help
            Print help information

    -s, --database-schema <DATABASE_SCHEMA>
            Database schema
             - For MySQL and SQLite, this argument is ignored.
             - For PostgreSQL, this argument is optional with default value 'public'.
            [env: DATABASE_SCHEMA=]

    -u, --universal-time
            Generate migration file based on Utc time instead of Local time

    -u, --database-url <DATABASE_URL>
            Database URL [env: DATABASE_URL=]

    -v, --verbose
            Show debug messages

After the fix:

➜ sea-orm-cli migrate generate -h
sea-orm-cli-migrate-generate
Generate a new, empty migration

USAGE:
    sea-orm-cli migrate generate [OPTIONS] <MIGRATION_NAME>

ARGS:
    <MIGRATION_NAME>    Name of the new migration

OPTIONS:
    -d, --migration-dir <MIGRATION_DIR>
            Migration script directory.
            If your migrations are in their own crate,
            you can provide the root of that crate.
            If your migrations are in a submodule of your app,
            you should provide the directory of that submodule. [default: ./migration]

    -h, --help
            Print help information

    -s, --database-schema <DATABASE_SCHEMA>
            Database schema
             - For MySQL and SQLite, this argument is ignored.
             - For PostgreSQL, this argument is optional with default value 'public'.
            [env: DATABASE_SCHEMA=]

    -u, --database-url <DATABASE_URL>
            Database URL [env: DATABASE_URL=]

        --universal-time
            Generate migration file based on Utc time instead of Local time

    -v, --verbose
            Show debug messages