Remove the possiility of numbers being generated as keys in maps/objects/dictionaries.

[Rovanion]

According to the GeoJSON specification:

GeoJSON is a format for encoding a variety of geographic data structures using JavaScript Object Notation (JSON) RFC7159

The GeoJSON specification RFC7159 in turn specifies that

An object structure is represented as a pair of curly brackets surrounding zero or more name/value pairs (or members). A name is a string.

In other words: In order for this generator to conform to the spec it cannot produce numbers as the keys/names in objects. And as is noted in the GeoJSON spec,

A Feature object has a member with the name "properties". The value of the properties member is an object (any JSON object or a JSON null value).