Bump execa from 3.4.0 to 4.0.0

Bumps [execa](https://github.com/sindresorhus/execa) from 3.4.0 to 4.0.0.
- [Release notes](https://github.com/sindresorhus/execa/releases)
- [Commits](sindresorhus/execa@v3.4.0...v4.0.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

npm-shrinkwrap.json

@@ -124,7 +124,7 @@
 		"eslint": "^6.8.0",
 		"eslint-config-google": "^0.14.0",
 		"eslint-plugin-jsdoc": "^15.12.2",
-		"execa": "^3.4.0",
+		"execa": "^4.0.0",
 		"jsdoc": "^3.6.3",
 		"mock-require": "^3.0.3",
 		"nyc": "^15.0.0",