Serialize:true should take priority over the OneToMany check for relationships

[igorT]

data/packages/ember-data/lib/serializers/json-serializer.js

Line 644 in ae6355a

if (this._canSerialize(key)) {

we should have a check for something like mustSerialize and account for it

data/packages/ember-data/lib/serializers/json-serializer.js

Line 656 in ae6355a

if (relationshipType === 'manyToNone' || relationshipType === 'manyToMany') {