reload the created snapshot before returing in create_snapshot! metho…

…d to prevent returing an invalid record

SnapshotItem has an uniqueness validation on `item_id`. This causes the
snapshot to be invalid after all SnapshotItems have been saved to the
database via `upsert_all`.
All records instanciated with `Snapshot#build_snapshot_item` are not
reloaded.

lib/active_snapshot/models/concerns/snapshots_concern.rb

@@ -34,7 +34,7 @@ def create_snapshot!(identifier: nil, user: nil, metadata: nil)
 
       SnapshotItem.upsert_all(new_entries.map{|x| x.delete("id"); x }, returning: false)
 
-      snapshot
+      snapshot.reload
     end
 
     class_methods do

test/models/snapshots_concern_test.rb

@@ -37,6 +37,7 @@ def test_create_snapshot!
 
     snapshot = @post.create_snapshot!(identifier: "foobar 1", user: @user, metadata: {foo: :bar})
     assert_not snapshot.new_record?
+    assert snapshot.valid?
 
     snapshot = @post.create_snapshot!(identifier: "foobar 2", user: @user)
     assert_not snapshot.new_record?