Compatilibity with Next.js

[Bathlamos]

Just an FYI that your library does not seem to be compatible with SSR on Next.js. I encounter the following error when rendering a page on the server side (where the window object isn't available):

[ error ] ReferenceError: window is not defined
    at Object.<anonymous> (/Users/bathlamos/my-project/node_modules/react-scrollspy-nav/dist/ScrollspyNav.js:1:224)
    at Module._compile (internal/modules/cjs/loader.js:955:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:991:10)
    at Module.load (internal/modules/cjs/loader.js:811:32)
    at Function.Module._load (internal/modules/cjs/loader.js:723:14)
    at Module.require (internal/modules/cjs/loader.js:848:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.react-scrollspy-nav 

I would at first thought this issue to be similar to #18 except that I'm already at React 16 and the error occurs at a different place.

[tolchai]

Here are possible solutions (in this case for Gatsby, but same problem) - https://www.gatsbyjs.org/docs/debugging-html-builds/#how-to-check-if-window-is-defined