AttributeError: 'int' object has no attribute 'startswith'

[swills]

Environment

• Python version: 3.7.7
• PyKwalify version: 1.7.0 (02b7e21)

Steps to Reproduce

1. pykwalify -s schema.yaml -d data.yaml

Schema

type: map
mapping:
  test:
    type: map
    mapping:
      0:
        type: str

Data

test:
  0: test

Expected Behavior

Validation Passed

Observed Behavior

Traceback (most recent call last):
  File "/usr/local/bin/pykwalify", line 11, in <module>
    load_entry_point('pykwalify==1.7.0', 'console_scripts', 'pykwalify')()
  File "/usr/local/lib/python3.7/site-packages/pykwalify/cli.py", line 98, in cli_entrypoint
    run(parse_cli())
  File "/usr/local/lib/python3.7/site-packages/pykwalify/cli.py", line 85, in run
    c.validate()
  File "/usr/local/lib/python3.7/site-packages/pykwalify/core.py", line 156, in validate
    self._start_validate(self.source)
  File "/usr/local/lib/python3.7/site-packages/pykwalify/core.py", line 198, in _start_validate
    root_rule = Rule(schema=self.schema)
  File "/usr/local/lib/python3.7/site-packages/pykwalify/rule.py", line 66, in __init__
    self.init(schema, "")
  File "/usr/local/lib/python3.7/site-packages/pykwalify/rule.py", line 443, in init
    func_mapping[k](v, rule, path)
  File "/usr/local/lib/python3.7/site-packages/pykwalify/rule.py", line 1180, in init_mapping_value
    rule.init(v, u"{0}/mapping/{1}".format(path, k))
  File "/usr/local/lib/python3.7/site-packages/pykwalify/rule.py", line 443, in init
    func_mapping[k](v, rule, path)
  File "/usr/local/lib/python3.7/site-packages/pykwalify/rule.py", line 1152, in init_mapping_value
    if k.startswith("regex;") or k.startswith("re;"):
AttributeError: 'int' object has no attribute 'startswith'

This is similar to #167 but slightly different. I think this is due to this bug:

yaml/pyyaml#98

Can be avoided by adding str() in the appropriate place, I can submit a pull request if you like.