Update `magic-string`

[rtritto]

Current version of magic-string 0.25.0 dependency use sourcemap-codec dependency that is deprecated.
In version 0.27.0 it's replaced with @jridgewell/sourcemap-codec.
magic-string dependency needs to be updated.

Steps to reproduce

• yarn init -y
• yarn set version canary
• yarn add @surma/rollup-plugin-off-main-thread
• Output:

➤ YN0000: ┌ Resolution step
➤ YN0061: │ sourcemap-codec@npm:1.4.8 is deprecated: Please use @jridgewell/sourcemap-codec instead
➤ YN0000: └ Completed
➤ YN0000: ┌ Fetch step
➤ YN0000: └ Completed
➤ YN0000: ┌ Link step
➤ YN0000: └ Completed
➤ YN0000: Done with warnings

[imnasnainaec]

@surma @RReverser Might one of you be available to bump the dependencies?

[Trickfilm400]

PR Reference: #57

What about creating a more maintained fork?