Pin sodium-universal to 3.0.2

[paul90]

A temp. fix for #72

This pins sodium-universal to 3.0.2 which will modify the version used by other dependencies.

npm ls sodium-universal currently shows

hyper-sdk@3.0.2
├─┬ hypercore-crypto@2.2.0
│ └── sodium-universal@3.0.3
└─┬ hypercore-protocol@8.0.7
  └─┬ simple-hypercore-protocol@2.1.1
    └─┬ noise-protocol@3.0.1
      ├─┬ hmac-blake2b@2.0.0
      │ └── sodium-universal@3.0.3  deduped
      └── sodium-universal@3.0.3  deduped

and becomes with this change

hyper-sdk@3.0.2
├─┬ hypercore-crypto@2.2.0
│ └── sodium-universal@3.0.2  deduped
├─┬ hypercore-protocol@8.0.7
│ └─┬ simple-hypercore-protocol@2.1.1
│   └─┬ noise-protocol@3.0.1
│     ├─┬ hmac-blake2b@2.0.0
│     │ └── sodium-universal@3.0.2  deduped
│     └── sodium-universal@3.0.2  deduped
└── sodium-universal@3.0.2

The only difference I see between 3.0.2 and 3.0.3 is an update to the version of sodium-javascript being used.

[paul90]

Closing as a probable underlying cause has been identified.