Add dist to gitignore

[niftylettuce]

When using np to publish this package, you can't because dist folder is not in the .gitignore file.

Changes not staged for commit:
 (use "git add <file>..." to update what will be committed)
 (use "git restore <file>..." to discard changes in working directory)
	modified: dist/stackframe.js
	modified: dist/stackframe.min.js
	modified: dist/stackframe.min.js.map