Allow for array transforms in config file to be passed to CLI

[stephenjwatkins]

According to the docs (https://github.com/jkphl/svg-sprite/blob/master/docs/command-line.md), a config file that's generated from the online config generator can be passed to the CLI. However, passing it the file wasn't able to read the SVGO transform plugins. This is because the CLI tries to do special string processing on the transform configuration.

This PR passes through the shape.transform config unless it is a string.

Example config file that was unable to process the svgo plugins:

{
  "dest": "dist",
  "shape": {
    "transform": [
      {
        "svgo": {
          "plugins": [
            { "removeUnknownsAndDefaults"    : false}
          ]
        }
      }
    ]
  },
  "mode": {
    "symbol": {
      "dest": ".",
      "sprite": "ui.svg"
    }
  }
}

[coveralls]

Coverage remained the same at 79.606% when pulling 793f2a6 on stephenjwatkins:master into 98585f6 on jkphl:master.