[fix] generate_key: fix issue where disabling symbols does not work
[fix] generate_key: fix issue where disabling symbols does not work

Code was doing `if (options.symbols && options.symbols === false)`, which obviously does not work. Fixed by checking for existing using `!== undefined` and squashed the `symbols` global.

Fixes #10.
auth0/speakeasy,markbao/speakeasy,speakeasyjs/libotp,mikepb/passcode,MCProHosting/speakeasy,speakeasyjs/speakeasy,mslosarek/speakeasy,speakeasyjs/libotp