fix: export `SignOptions` type

[stefansundin]

Hello,

I want to be able to import this type since I am calling some of the functions in this package.

I think this makes sense, especially since the sister-package @electron/notarize exports the NotarizeOptions type. https://github.com/electron/notarize/blob/11fcb0bc8ccb02a47c0a221f677b457f14d58fbf/src/index.ts

[continuous-auth[bot]]

:tada: This PR is included in version 1.0.5 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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