Change one file's cover image

[RogerWenXin]

Change one file's cover image and do not generate new file.

command line usage:

SublerCli -dest /Users/roger/Movies/a/sample2.mp4 -metadata {'Cover Art':'/Users/roger/Movies/a/sample.jpg'}

but this node-subler cannot do it.

I make some changes, for referrence:

and this dest checking is unnecessary, we just need overwite file.
after some modification:

and source is not necessary filed, should check it:

Some property should keep default value same as subler-cli, such as "optimize" etc. They should be false as default.

[SmolSoftBoi]

Would you like to open a PR?