doc: fix name of the flag in `initialize()` docs
--loader is an undocumented flag, the rest of the docs uses --experimental-loader to design that flag (--loader was kept as an undocumented alias to avoid a breaking change).
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--loader is an undocumented flag, the rest of the docs uses --experimental-loader to design that flag (--loader was kept as an undocumented alias to avoid a breaking change).