Make the pip hack script compatible with pip 18.1
Make the pip hack script compatible with pip 18.1

It [moved](https://github.com/pypa/pip/commit/a5a07fe61c4861c58fded7420c929d56cde11a89) the from_line method in a backwards-incompatible way. This should resolve the remainder of #133.

My Python is pretty atrophied, but I tested this against the following recipe and it converged successfully.

```ruby
apt_update 'default'

python_runtime '2'

python_virtualenv '/tmp/piplatest' do
  python '2'
end

python_virtualenv '/tmp/pip18' do
  python '2'
  pip_version '18.0'
end

python_virtualenv '/tmp/pip10' do
  python '2'
  pip_version '10.0.1'
end

python_virtualenv '/tmp/pip9' do
  python '2'
  pip_version '9.0.3'
end
```

poise/poise-python