fix(migrations): Remove unexpected shell call

This patch removes the call of `/usr/bin/env` when calling the migration
script in favour of using the processes own nodejs invocation path.

This should drop the requirement for `/usr/bin/env` to exist on a
system/in a container that runs hedgedoc.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

lib/migrations/20200321153000-fix-account-deletion.js

@@ -3,7 +3,7 @@ const { spawnSync } = require('child_process')
 const path = require('path')
 module.exports = {
   up: function (queryInterface, Sequelize) {
-    const cleanup = spawnSync('./bin/cleanup', { cwd: path.resolve(__dirname, '../../') })
+    const cleanup = spawnSync(process.argv[0], ['./bin/cleanup'], { cwd: path.resolve(__dirname, '../../') })
     if (cleanup.status !== 0) {
       throw new Error('Unable to cleanup')
     }