Version bump for bytestring

Hi,

First, thank you very much for writing this useful package and making it available!  I was incredibly pleased when I ran into it because it provided exactly what I needed without requiring any effort on my part.

The new version of GHC bumps bytestring to 0.10, which means that sequential-index no longer compilers.  In the commit attached to this note I bumped the bound to < 0.11 and the version of sequential-index to 0.2.0.1.  I ran both the tests that you provide and the tests in my project which depends on sequential-index, so everything seems to work just fine with the new version of bytestring.

If you would upload a version of sequential-index to Hackage that works with the new GHC (either using my patch or one of your own making), then I would greatly appreciate it.  Alternatively, if you don't want to deal with maintenance of this package anymore, then I would be happy to either take it off your hands or become a co-maintainers so I can take care of these kinds of necessary updates directly so that no effort is required on your part.  :-)

Cheers,
Greg