Add "inbox" and "followers" to JSON-LD context

[acka47]

Fixes #87

[acka47]

I think there is something wring with the test infrastructure. All tests fail to run with this message:

Test suite failed to run

[BABEL] /home/runner/work/skohub-vocabs/skohub-vocabs/test/{test}.test.js: Cannot find module '@babel/compat-data/corejs3-shipped-proposals'

Please help, @literarymachine .

[dr0i]

I think we can fix it leaving @literarymachine in parental leave ...
To begin with, it npm test works on our machines even using your branch (one must stop the skohub-vocabs daemon, though, for the test instance uses the same port when testing webHookServer. TODO: document this).
Second, e.g. laravel needs a newer babel/preset-env lib ,which may be installed on the github test environment. We use <v7.9.

[dr0i]

@acka47 as the last commit fixed the github test - ping if this PR ready to be merged and deployed.

[acka47]

+1 Please merge and deploy

[dr0i]

Merged and deployed, but see #87 for further questions.