Environments:

• Prettier Version: 1.16.4
• Running Prettier via: CLI (package.json script)
• Runtime: Node.js 8.11.3
• Operating System: MacOS 10.13.6

Steps to reproduce:

N/A

Expected behavior:
That when provided with an option such as --cache, prettier only process new or changed files. See eslint for example.

Actual behavior:
Prettier processes all files, whether they have changed or not.