exec specs for all dialects

spec/associations/mixin.spec.js

@@ -2,13 +2,16 @@ if (typeof require === 'function') {
   const buster    = require("buster")
       , Helpers   = require('../buster-helpers')
       , Sequelize = require('../../index')
+      , dialects  = Helpers.getSupportedDialects()
 }
 
 buster.spec.expose()
 
-describe('Mixin', function() {
+dialects.forEach(function(dialect) {
+  describe('Mixin@' + dialect, function() {
     before(function(done) {
       Helpers.initTests({
+        dialect: dialect,
         beforeComplete: function(sequelize) {
           this.sequelize = sequelize
         }.bind(this),
@@ -27,4 +30,5 @@ describe('Mixin', function() {
         expect(User.getAssociation(Task).target).toEqual(Task)
       })
     })
+  })
 })