Company custom data is incorrectly passed to Intercom API

The json the library generates for Company's custom properties is not working properly with Intercom API.

If your add **email** custom property the json generated is:
```
{
  "custom_data" : {
    "team_mates" : 7,
    "app_name" : "Genesis",
    "monthly_spend" : 155.5
  },
  "created_at" : 1270000000,
  "last_seen_user_agent" : "ie6",
  "email" : "john.doe@example.com",
  "user_id" : "abc123",
  "last_impression_at" : 1300000000,
  "last_seen_ip" : "1.2.3.4",
  "name" : "John Doe",
  "companies" : [
    {
      "id" : "6",
      "name" : "Intercom",
      "custom_data" : {
         "email" : "jhon@doe.com"
      }
    }
  ]
}
```
when it should be
```
{
  "custom_data" : {
    "team_mates" : 7,
    "app_name" : "Genesis",
    "monthly_spend" : 155.5
  },
  "created_at" : 1270000000,
  "last_seen_user_agent" : "ie6",
  "email" : "john.doe@example.com",
  "user_id" : "abc123",
  "last_impression_at" : 1300000000,
  "last_seen_ip" : "1.2.3.4",
  "name" : "John Doe",
  "companies" : [
    {
      "id" : "6",
      "name" : "Intercom",
      "email" : "jhon@doe.com"
    }
  ]
}
```