5.1.11

• Adjust Symbol null check in shim-array

5.1.9

Fix WillChange listeners

• Add specs for addBeforeOwnPropertyChange
• Change willChangeListenersRecord to be a
  WillChangeListenersRecord so the handler names include
  ‘Will’ e.g handlePropertyWillChange, handleFooWillChange

5.1.8

• Make Set.size observable in IE11 and under
• Fix a regression managing map listeners