Add SingleLineComment support to object

[BrentSouza]

We use this library to parse modules and stumbled upon an error when trying to parse a variable declaration for an object type that contained comments on some of the properties, e.g.:

variable "foo" {
  type = object({
    # this prop is really important for reasons
    bar = string
    # this one...who knows
    baz = string
}

I made a very small change to add support for SingeLineComments into the definition for ObjectTypeProperty. I'm not sure if this is the correct thing to do, but I added a test case and things are passing. Hurray!