Allow not writing initialize#arguments property in service.vvisp.json

[JhChoy]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[x] Feature request
[ ] Documentation issue or request
[ ] Other... Please describe:

Current behavior

If we describe service.vvisp.json like:

  "ContractA": {
      "path": "path/to/your/Contract.sol",
      "initialize": {
        "functionName": "initialize"
      }
    }

It makes error! So we have to describe like:

  "ContractA": {
      "path": "path/to/your/Contract.sol",
      "initialize": {
        "functionName": "initialize",
        "arguments": []
      }
    }

Expected behavior

Allow the first describe.

Environment

vvisp version: v0.1.9


Environment:
- Node version: v8.11.2
- Operating system: Mac OSX