test: use snapshot-diffs

[tivac]

Description

Using snapshot-diffs where possible, also changes the output from test-utils/read-dir.js to look a little cleaner.

Motivation and Context

Tidies up snap files and better verifies that changes actually happened between runs.

How Has This Been Tested?

npm test

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[TravisBuddy]

Hey @tivac,
Something went wrong with the build.

TravisCI finished with status errored, which means the build failed because of something unrelated to the tests, such as a problem with a dependency or the build process itself.

View build log

TravisBuddy Request Identifier: 2d3689a0-513b-11e9-977c-5d859f4a0935