swaggerfilter.py script throws runtime error with python3

When I run build with python3, I am getting the following runtime error:

File "/Users/asi/tools/argo-events-client-java/./hack/swaggerfilter.py", line 29, in main
for k in defs.keys():
RuntimeError: dictionary changed size during iteration

I have to modify the script to:

```
keys = defs.keys()
if sys.version_info[0] == 3:
keys = defs.copy().keys()

for k in keys:
...
```

Start in hack/swaggerfilter.py at line 29 and reproduce the failure by running the build with Python 3. Inspect the definitions iteration and verify that the build completes without the dictionary-changed-during-iteration runtime error.

Written by the indexing model from the issue text.