is_binary should check more than just ce-specversion

## Expected Behavior
```python
from cloudevents.sdk.converters.binary import NewBinaryHTTPCloudEventConverter
cnvtr = NewBinaryHTTPCloudEventConverter()
assert not cnvtr.can_read({"ce-specversion": "1.0"})
```

## Actual Behavior
```python
cnvtr.can_read({"ce-specversion": "1.0"})
```
will return true because it only checks for ce-specversion and not other required versions. 
