Fix wrong option name in en/blog/release/v12.12.0.md

[mysticatea]

I found the option name in the blog post is wrong.

$ node --source-map-support
C:\Program Files (x86)\Nodist/v-x64/12.12.0/node.exe: bad option: --source-map-support

$ node --enable-source-maps
Welcome to Node.js v12.12.0.
Type ".help" for more information.
>

[nschonni]

Thanks, looks like the naming changed between the initial PR and description and the final commit

[Trott]

Refs: nodejs/node#29959
Refs: nodejs/node#29960

I suspect they'll both be 👍 on it, but /ping @bcoe @BridgeAR anyway

[Trott]

Actually, this is kind of important (as people are reading this blog post now but not so much in a week) so I'm going to land this right away. We can always change it again if need be.

[BridgeAR]

Thank a lot for the fix.

[bcoe]

@Trott thanks for catching this and fixing it.

[bcoe]

likewise @mysticatea, thank you both.