[#3] Remove hardcoded snyk path

[asos-craigmorten]

Issue

Fixes #3

Details

• fix: don't rely on hardcoded paths to snyk binary

Update relies on user having npx installed, which will be the case since version 5.2.0 of npm - https://nodejs.dev/learn/the-npx-nodejs-package-runner

We use https://docs.npmjs.com/cli/v8/configuring-npm/package-json#engines to ensure that this condition is met.

CheckList

• PR starts with [ISSUE_ID].
• Has been tested (where required) before merge to main.