Update rollup and rollup-plugin-terser

[martin frances]

I have just enabled automated security audits on my github account and the bot reported a security warning for my local copy of d3-geo which I would like to fix upstream.

serialize-javascript has a high severity warning

which is pulled in as a result of our outdated use of rollup-plugin-terser

my proposal it we bump the major version of both rollup and rollup-plugin-terser

When I test locally every works smoothly... I am about to file a PR.

here is the diff of package.json

• "rollup": "1",
• "rollup-plugin-terser": "5",

• "rollup": "^2.45.2",
• "rollup-plugin-terser": "^7.0.2",

[Mike Bostock]

Fixed in #238.

[martin frances]

Thank you