Fix release script

[dmethvin]

This is a meta-ticket for the problems I encountered during the 1.11.1/2.1.1 release, some of these will be jquery-release issues and others with core's release.js script.

• The 1.x release tries to update jquery.js and jquery-latest.js on the CDN and ​fails, we if we're not going to update these anymore and freeze them at 1.11.1 we can just remove that from core's release.js.

• I've now had npm publish --tag fail on me in two different releases. It worked for the 2.x but ​failed on 1.x. As a result I ended up doing the subsequent steps manually there. (Note that npm publish --tag 1.x worked fine manually both times!) Since npm is independent from the later steps there should be an idea of "error but you can continue" in jquery-release to simplify error recovery and minimize the mess.

• The CDN zip files created by release.js were empty (0 bytes) for the 2.x release. I didn't get that far with 1.x because of the npm error.

• The build script never came back to a shell prompt even after I got the ​"complete" message; perhaps related to why the zip files were empty.