Fix invalid field name on OctetKeyParameters (#256)
Fix invalid field name on OctetKeyParameters (#256)

RFC 7518 defines the parameters for symmetric keys to have the 'k' (Key
Value) parameter (Section 6.4.1). The OctetKeyParameters structure
unfortunately has it defined as "value".

This change should allow parsing of jwks.json files with a symmetric key
while keeping the same api.

I've also added a simple test to validate this works as expected.
Keats/jsonwebtoken