String diffs don't invert properly

[novemberborn]

In AVA, when diffing snapshots the gutters are inverted. This doesn't invert the string diff colors though. Compare the output for these tests:

import test from 'ava'

test('snapshot diff', t => {
  t.snapshot(`\n${Date.now()}\n`, 'the - value should be less than the + value')
})

test('direct diff', t => {
  t.is(`\n${Date.now() - 42e5}\n`, `\n${Date.now()}\n`)
})

I realized this previously but hadn't yet filed the issue. Example via avajs/ava#1558.

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• #69 Invert string diffs

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