.pipe broken in browser due to process check

https://github.com/caolan/highland/blob/master/lib/index.js#L769
This line assumes that process exists (it should have a typeof process !== 'undefined' check) as a variable and will break spectacularly if you use .pipe in a browser. :( If I comment out the line, piping works fine.

Start at lib/index.js line 769 and reproduce the failure by using .pipe in a browser environment. Check the assumption that process exists there, then verify that browser piping works after the issue is addressed.

Written by the indexing model from the issue text.