swaggerfilter.py script throws runtime error with python3

[antoniosi]

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:
          ...

[antoniosi]

I will create a PR for the fix soon.