Bump Vagrant requirement to 1.8.x
Bump Vagrant requirement to 1.8.x

The use of the `env` option for the `shell` provisioner requires at least this
version. Or the following errors will be raised:

    There are errors in the configuration of this machine. Please fix
    the following errors and try again:

    shell provisioner:
    * The following settings shouldn't exist: env
    * The following settings shouldn't exist: env
    * The following settings shouldn't exist: env
    * The following settings shouldn't exist: env

jimconner/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf