Fix gitignore

[MarcusOtter]

Remove lock file gitignores

Reasons:

• "Do I commit the package-lock.json file created by npm 5?" (https://stackoverflow.com/questions/39990017/should-i-commit-the-yarn-lock-file-and-what-is-it-for) and
• "Should I commit the yarn.lock file?" (https://stackoverflow.com/questions/39990017/should-i-commit-the-yarn-lock-file-and-what-is-it-for)
• The svelte rollup template does not have these files in the gitignore. https://github.com/sveltejs/template/blob/master/.gitignore

Fix gitignore build path

Reasons:

• It was changed with https://github.com/sveltejs/template-webpack/issues/34 and https://github.com/sveltejs/template-webpack/pull/36 but the gitignore was forgotten.