Update library.md
Update library.md

There is no https://github.com/google/sandboxed-api/blob/master/sandboxed_api/examples/zlib/lib/sandbox.h - it either wasn't commited or we meant different sandbox.h here. For now I linked to sum's sandbox.h
google/sandboxed-api,google/sandboxed-api,google/sandboxed-api,google/sandboxed-api