Use type "int" for argparse type field instead of a string
Use type "int" for argparse type field instead of a string

This suppresses the following deprecation warnings:

```
/usr/lib/python3.5/site-packages/flaky/_flaky_plugin.py:356: DeprecationWarning: type argument to addoption() is a string 'int'. For parsearg this should be a type. (options: ('--max-runs',))
  help="If --force-flaky is specified, we will run each test at "
/usr/lib/python3.5/site-packages/flaky/_flaky_plugin.py:366: DeprecationWarning: type argument to addoption() is a string 'int'. For parsearg this should be a type. (options: ('--min-passes',))
  help="If --force-flaky is specified, we will run each test at "
```
box/flaky,Jeff-Meadows/flaky