Remove hard dependency on npm 3.x.x

[peh]

When trying to use a recent version of npm the install fails with:

> npm install
npm ERR! code EBADENGINE
npm ERR! engine Unsupported engine
npm ERR! engine Not compatible with your version of node/npm: lottie-react-web@2.2.2
npm ERR! notsup Not compatible with your version of node/npm: lottie-react-web@2.2.2
npm ERR! notsup Required: {"npm":"^3.0.0"}
npm ERR! notsup Actual:   {"npm":"7.5.3","node":"v15.9.0"}

using npm install --engine-strict false simply works.

It looks to me as if this is an old requirement that is not valid anymore.