upgrade sign to remove circular dependency

ok apparently my previous fix didn't fix the circular dependency issue I had in browserify sign, the reason I wasn't able to find it like I should was that I was only able to reproduce it when, due to npm deduping, readable-stream was not in the same directory as browserify-sign so every time I went to fix it and used npm-link readable stream *would* be in the directory and the build would work.  Just changed it to use stream instead of readable stream and I tested by manually changing the dep in browserify in the node_modules folder of a package to use calvinmetcalf/crypto-browserify#circular-dep-sign and then npm installing it all and verifying it works.