fix(url): Conform to Rollup type definitions.

[seivan]

Rollup Plugin Name: url

This PR contains:

• bugfix
• other

Are tests included?

• yes

Breaking Changes?

• no

Description

Conform to Rollup type definitions to silence compiler errors, as they expect a plugin name and it's expected/advised on the docs.

Current workaround is:

        {
            name: "url",
            ...url({
                limit: 0,
                include: defaultAssetTypes,
                fileName: '[dirname][name]_[hash][extname]',
                sourceDir: path.join(__dirname, 'src')
            })
        },

or more succinct and error prone:

        url({
            limit: 0,
            include: defaultAssetTypes,
            fileName: '[dirname][name]_[hash][extname]',
            sourceDir: path.join(__dirname, 'src')
        }) as any,

Also, exporting defaultInclude as I'd like to extend the defaults instead of redefining them.
Edit: Got rid of that, since I guess you don't want to mix default and named export, understandable.