chore: upgrade sequelize (#965)

* 0.18.0

* chore: Upgrade sequelize 4 -> 5

* fix: migrations v5 support

* fix: Majority of test failures

* fix: the rest of v5 tests

server/models/Team.js

@@ -131,7 +131,6 @@ Team.prototype.removeAdmin = async function(user: User) {
       teamId: this.id,
       isAdmin: true,
       id: {
-        // $FlowFixMe
         [Op.ne]: user.id,
       },
     },