Do not store Password warning in db dump

Hello,

Thanks for sharing your software. I use mysql56 from homebrew on a Mac, and when dumping local db 
"Warning: Using a password on the command line interface can be insecure." is added to the dump file, and then import fails. The way I've solved it here is obviously not fancy, but it does the trick for me.

Let me know if you need any help with merging this in or testing other use cases if you don't have access to an environment where you can reproduce this.