Add shebang to run.js (#528)

Fixes running the hooks through Yarn (which doesn't call husky-run as a
script).

run.js

@@ -1,3 +1,4 @@
+#!/usr/bin/env node
 /* eslint-disable @typescript-eslint/no-var-requires */
 const pleaseUpgradeNode = require('please-upgrade-node')
 const pkg = require('./package.json')