Update str_to_bool function to include 'nope' as a valid false value

[tkosman]

Let’s keep things fair.
If we're parsing 'yup' and 'yep' as bool type True.
Definitely 'nope' belongs to bool type False.

Example:

import os
import sanic

os.environ["SANIC_NOPE"] = "nope"

app = sanic.Sanic("Nope")

@app.route("/")
async def nope(request):
    return sanic.response.json({"NOPE IS": app.config.get("NOPE")}) # {NOPE IS: false}


if __name__ == "__main__":
    app.run()