Fix YAML::Newline in a sequence or map.

Inside of a sequence or map, `YAML::Newline` wouldn't reset the collection state, which would cause behavior like this:

```
nodeA:   
    k: [{i: 0},
 {i:1},
  ]NodeB:
    k: [{i: 0},
 {i:1},
  ]
```

src/emitterstate.cpp

@@ -179,6 +179,9 @@ void EmitterState::EndedGroup(GroupType::value type) {
   m_globalModifiedSettings.restore();
 
   ClearModifiedSettings();
+  m_hasAnchor = false;
+  m_hasTag = false;
+  m_hasNonContent = false;
 }
 
 EmitterNodeType::value EmitterState::CurGroupNodeType() const {