Remove github OAuth token

[danez]

Summary

Fixes #612
This does not call github.authenticate() if there is no token provided. Maybe even removing the call at all now that yarn is OS?

This only fixes the authentication issue, after I fixed this it seems yarn is trying to download an rpm file on my mac. Going to look into this next.

info Downloading asset "yarn-0.15.0-1.noarch.rpm" from release "v0.15.0"
error https://api.github.com/repos/yarnpkg/yarn/releases/assets/2456563?access_token=undefined: invalid tar file
    at Extract.Parse._startEntry (/Users/danieltschinder/.yarn/node_modules/tar/lib/parse.js:149:13)
    at Extract.Parse._process (/Users/danieltschinder/.yarn/node_modules/tar/lib/parse.js:131:12)
    at BlockStream.<anonymous> (/Users/danieltschinder/.yarn/node_modules/tar/lib/parse.js:47:8)
    at emitOne (events.js:77:13)
    at BlockStream.emit (events.js:169:7)
    at BlockStream._emitChunk (/Users/danieltschinder/.yarn/node_modules/block-stream/block-stream.js:145:10)
    at BlockStream.flush (/Users/danieltschinder/.yarn/node_modules/block-stream/block-stream.js:70:8)
    at BlockStream.end (/Users/danieltschinder/.yarn/node_modules/block-stream/block-stream.js:66:8)
    at Extract.Parse.end (/Users/danieltschinder/.yarn/node_modules/tar/lib/parse.js:86:23)
    at UnpackStream.onend (_stream_readable.js:498:10)

Test plan

Well, there are tests for self-update but seems they are disabled. I try to disable them in the upcoming PR :)

[sebmck]

Awesome! Could you remove the token stuff all together please? We wont need it now that we're open source.

[danez]

I changed it, but for some reason I cannot squash them locally because, I always have changed files in my working copy on a mac and cannot get rid of them (Some CRLF vs. LF) problem it seems Seems a new checkout again fixed it

[sebmck]

Thank you! @bestander can you please review since you're most familiar with this piece!

[bestander]

@danez, could you check if tests are passing if you undisable them?
Also feel free to startup a discussion whether yarn should be evergreen and selfupdate automatically

[danez]

No, see #676. For now I also did this change there to see that the tests work, we might close this PR here if you want the tests to run for this change.

[danez]

Okay i close this in favor of #676