set expandGitHubIssueLinks to inverse of noGitHubIssueLinking

[horihiro]

This PR contains handling noGitHubIssueLinking option and variable expandGitHubIssueLinks properly.

According to commandar, noGitHubIssueLinking can be true or undefined, cannot be false because the option name doesn't start with --no-.
So expandGitHubIssueLinks is same.
https://github.com/tj/commander.js#other-option-types-negatable-boolean-and-booleanvalue

On current implementation, the expandGitHubIssueLinks is always true after this conditional operator if expandGitHubIssueLinks cannot be false, as reported in #542

vscode-vsce/src/package.ts

Lines 441 to 442 in f186af2

	this.expandGitHubIssueLinks =
	typeof options.expandGitHubIssueLinks === 'boolean' ? options.expandGitHubIssueLinks : true;

[joaomoreno]

A better fix is to just adopt the --no syntax: 83163ed

Thanks though!