[bug] threat intel - ParamValidationError: Parameter validation failed: Invalid type for parameter

### Full Traceback

```
Traceback (most recent call last):
File "/var/task/stream_alert/rules_engine/threat_intel.py", line 144, in _process_ioc_values
query_result = self._query(query_values)
File "/var/task/stream_alert/rules_engine/threat_intel.py", line 229, in _query
_run_query(values, results)
File "/var/task/backoff/_sync.py", line 48, in retry
ret = target(*args, **kwargs)
File "/var/task/backoff/_sync.py", line 99, in retry
ret = target(*args, **kwargs)
File "/var/task/stream_alert/rules_engine/threat_intel.py", line 205, in _run_query
'ProjectionExpression': self.PROJECTION_EXPRESSION
File "/var/task/botocore/client.py", line 357, in _api_call
return self._make_api_call(operation_name, kwargs)
File "/var/task/botocore/client.py", line 634, in _make_api_call
api_params, operation_model, context=request_context)
File "/var/task/botocore/client.py", line 682, in _convert_to_request_dict
api_params, operation_model)
File "/var/task/botocore/validate.py", line 297, in serialize_to_request
raise ParamValidationError(report=report.generate_report())
ParamValidationError: Parameter validation failed:
Invalid type for parameter RequestItems.airbnb_streamalert_threat_intel_downloader.Keys[1].ioc_value.S, value: True, type: , valid types:
```

## Desired Change

Fix issue

Start in stream_alert/rules_engine/threat_intel.py at _process_ioc_values, _query, and _run_query, following the traceback to the failing request. Reproduce the threat-intel query and trace how the boolean IOC value reaches RequestItems; done means the request no longer sends an invalid type where a string is required.

Written by the indexing model from the issue text.