bootstrap.js: update to HTTPS, add Java-8 update site

[frauzufall]

This PR updates the bootstrap.js script to HTTPS and adds the Java-8 update site since the HTTPS related updater JARs are also there.

I tested it by running the Fiji's build.sh script (without the deployment part) after replacing the link to this bootstrapJ8.js script with the one from this PR, checking for no errors during the execution and then I started the Linux64 version which indeed used HTTPS links by default.

I guess this script got manually copied to https://downloads.imagej.net/bootstrapJ8.js or is there another source for the bootstrapJ8.js script?

@ctrueden mentioned here that we might break someone's Java 6 installation - I'm not sure how since the bootstrapJ8.js script already created Fiji's with Java-8 enabled. Is this bootstrap.js script in this repository used for anything else?

[turekg]

I've diff'd this new version with the bootstrapJ8.js script which is being used by the the fiji build script. After I changed http -> https in the latter there is a pertinent difference still. bootstrapJ8.js is till using https://update.imagej.net/jars instead of https://sites.imagej.net/Java-8/jars/. I would recommend that the fiji build.sh script be updated to always reference the bootstrap script in this repo (master branch). In the long run bootstrapJ8.js could be done away with. We should merge this ASAP

[frauzufall]

Closing this because, if I remember correctly, we are not using the bootstrap.js script for building Fiji any more. Can we maybe just delete the script @ctrueden?

[ctrueden]

I cannot find any uses of bootstrap.js or bootstrapJ8.js across the codebase, so I removed the script from this repository. However, I'll leave bootstrapJ8.js on downloads.imagej.net, just in case anyone is still making use of it. Officially unsupported now, though! 🍻