Use more explicit bit-shifting

We're creating 64-bit ints, so let's use 64 (rather than the 0-indexed
63) in the math.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Update bigint dependency

0.3.9 has some node-waf installation issues and fails with more recent
versions of Node.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Reduce strictness in JavaScript spec

While the stricter check used to work, it no longer does.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Bump Node library

Updates Node and bigint dependencies.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>