Version constraint in subnet,vnet, and remote-state-storage module

[grayjeremy]

the subnet, vnet, and remote-state-storage modules uses a version constraint that excludes version 0.12.0, referenced below. I had assumed that the version constraint listed was good for versions >= 0.11.1 and < 1.0.0, per this article. This may not be the case. On another note, this module doesn't really seem to add any value to the subnet provider and has no documentation on usage. This issue peeled off of #16.

terraform {
  required_version = "~> 0.11.1"
}