doc: fix JSON generation for aliased methods

Currently assert/assert.ok currently has the following signature:

    "signatures": [
      {
        "params": [
          {
            "name": "value"
          },
          {
            "name": "message])"
          },
          {
            "name": "assert.ok(value"
          },
          {
            "name": "message",
            "optional": true
          }
        ]
      }
    ]

The heading reads

    assert(value[, message]), assert.ok(value[, message])

Split them into two sections to make it working.

PR-URL: https://github.com/nodejs/node/pull/4871


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>