Use opencollective-postinstall instead of opencollective

[topaxi]

Summary

Use opencollective-postinstall instead of opencollective

Explain the motivation for making this change. What existing problem does the pull request solve?

See #231 (comment)

Requirements

Make sure these boxes are checked:

• link to an issue
• tests are updated (added/changed/removed)
• tests run successfully (local)
• tests run successfully (TravisCI)
• please follow this styleguide for this pr title

[orizens]

@topaxi after a closer look - it seems like moving opencollective to devDependencies disables the message for contribution when installing ngx-infinite-scroll.

[topaxi]

I see, that is very unfortunate because opencollective pulls in a lot of dependencies :(

[mnahkies]

@topaxi wouldn't these be shaken out of production builds anyway? Still not ideal, but I wouldn't have expected it to affect bundle sizes

[topaxi]

This wasn't about bundle size but installation size. Sometimes one is on the road and wants to develop and being in a train or on some bad mobile or wifi connection the size of packages and amount of dependencies can cripple local installation with npm install a lot.

[anteq]

Hey, how about substituting opencollective postinstall with opencollective-postinstall? It looks like it's the new recommended package with almost no dependencies. That also prevents "Permission denied" crashes on some CI servers:
opencollective/opencollective-postinstall#15

[topaxi]

I have updated the PR to use opencollective-postinstall.