Update advanced_foreword.rst

I think the doc is supposed to read, "Because of that, Flask has a few design choices that some people might find surprising or unorthodox."

Otherwise, it could possibly mean, "Because of that, Flask has few design choices that people would find surprising or unorthodox."

Or perhaps even less ambiguous, "Because of that, Flask has few surprising or unorthodox design choices."
Merge pull request #1064 from kekumu/patch-adv-foreword

Ambiguity in Advanced Foreword