Add pretty-format as devDep

Typings use `import {OptionsReceived as PrettyFormatOptions} from 'pretty-format'`
Fix testing-library#694

Author: samtsai

package.json

@@ -54,6 +54,7 @@
     "dtslint": "3.6.9",
     "kcd-scripts": "^6.2.0",
     "npm-run-all": "^4.1.5",
+    "pretty-format": "^25.5.0",
     "react": "^16.13.1",
     "react-dom": "^16.13.1",
     "rimraf": "^3.0.2"