[FIX] Change old 'rocketbot' username to 'InternalHubot_Username' setting

[ramrami]

@RocketChat/core

Before :

when typing an unknown command, rocketbot respond, we're expecting InternalHubot_Username

After :

[CLAassistant]

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[sampaiodiego]

oh, you found a missing rocketbot 😂

I'm just thinking the impact of making the setting public, otherwise LGTM

[ramrami]

@sampaiodiego I just found another one here 😄