Gordon apply error in 0.3.0 (works in 0.2.1)

```
$ gordon apply --stage=dev
Applying project...
Enter MFA code: [...enter code...]
Traceback (most recent call last):
File "/usr/local/bin/gordon", line 9, in
load_entry_point('gordon==0.3.0', 'console_scripts', 'gordon')()
File "/usr/local/lib/python2.7/dist-packages/gordon/bin.py", line 106, in main
getattr(obj, options.func)()
File "/usr/local/lib/python2.7/dist-packages/gordon/core.py", line 426, in apply
context.update(self.collect_parameters())
File "/usr/local/lib/python2.7/dist-packages/gordon/core.py", line 475, in collect_parameters
context=context
File "/usr/local/lib/python2.7/dist-packages/gordon/utils.py", line 190, in convert_cloudformation_types
cf_data[k] = ', '.join(v)
TypeError: sequence item 0: expected string, dict found
```

The same project/config work fine in 0.2.1.
NOT using bucket event sources at all.
I'm not into python so just tell me what you need to debug the issue there... :)

Start with gordon/core.py at collect_parameters and follow the call into gordon/utils.py at convert_cloudformation_types. Reproduce `gordon apply --stage=dev` with the reported project and compare behavior between versions 0.2.1 and 0.3.0; done means the apply completes without the TypeError.

Written by the indexing model from the issue text.