Modify 'depth' attribute to follow enum pattern

[zhanif3]

I am proposing to alter the 'depth' attribute in 'dictionary,json' to better conform to the pattern of other enum elements in the same file. This would most likely result in a breaking change.

Per #422, there was an action taken to alter enum elements to set id 0 to represent 'Unknown' and 99 to represent 'Other'. This was not applied to the 'depth' attribute, resulting in the only instance of a non-numbered enum. In the thread around issue 422 above, this was noted as a deliberate choice "usually used when the values are defined by external standard". However, this is the appears to be the only instance in the dictionary where this is the case.

I am proposing that depth be changed to conform to style suggested by the other enums, retaining the textual caption. This will remove ambiguity when generating language bindings for the schema.

The change is as follows:

    "depth": {
      "caption": "CVSS Depth",
      "description": "The CVSS depth represents a depth of the equation used to calculate CVSS score.",
      "enum": {
        "0": {
          "caption": "Base"
        },
        "1": {
          "caption": "Environmental"
        },
        "2": {
          "caption": "Temporal"
        }
      },
      "type": "integer_t"
    },