Please update pinned versions

AWS CLI is unique on my system in pinning many things to specific versions, and pinning them to versions that are very old and no longer in common usage by "most people". I tested just now with the latest aws cli versions available.

And in particular from a security standpoint, pinning versions for security packages like `cryptography` and `rsa` opens security holes if they cannot be upgraded to always be current.

Would be great to see AWS CLI remove the pins because they create ongoing, irresolvable conflicts.

**awscli==2.1.26**
```
- colorama [required: >=0.2.5,<0.4.4, installed: 0.4.4]
- docutils [required: >=0.10,<0.16, installed: 0.16]
- cryptography [required: >=2.8.0,<=2.9.0, installed: 3.4.4]
- ruamel.yaml [required: >=0.15.0,<0.16.0, installed: 0.16.12]
- wcwidth [required: <0.2.0, installed: 0.2.5]
- prompt-toolkit [required: >=2.0.0,<3.0.0, installed: 3.0.16]
```

**awscli==1.19.7**
```
- docutils [required: >=0.10,<0.16, installed: 0.16]
- PyYAML [required: >=3.10,<5.4, installed: 5.4.1]
- colorama [required: >=0.2.5,<0.4.4, installed: 0.4.4]
- rsa [required: >=3.1.2,<=4.5.0, installed: 4.7]
```