Keep cursor shown in ProgressReporter so it isn't hidden in debugger.

@os97673 for review
cc @csaunders

Fixes #76

## Problem

When using the ProgressReporter, the cursor will be hidden when in the debugger.

This can be reproduced by starting the debugger in a test as follows

```
require 'minitest/autorun'
require "minitest/reporters"
Minitest::Reporters.use! Minitest::Reporters::ProgressReporter.new

require 'byebug'

class DebugTest < Minitest::Test
  def test_1
  end

  def test_debugger
    debugger
  end
end
```

The first test was added to make sure the progress bar is printed before the debugger line, since that was what was hiding the debugger.

## Solution

Avoid hiding the cursor.

The cursor will just be visible at the end of the line with the progress bar.