npm v7.10.0 seems to ignore postinstall script

[lidel]

Just for visibility, ipfs binary does not seem to be downloaded with npm v7.10.0. Running npx npm@6 ci fixes the problem, and I saw a bunch of "postinstall" related regressions in v7, so I assume it's not something on my end.

cc @achingbrain @hugomrdias as this will impact all aegir-based projects – they all fetch go-ipfs via this package