"Query parameters" form shows wrong input fields if query contains "03:31" style times

Datasette version `0.58.1`.

I'm guessing this is a bug in the code that looks for `:param`-style query parameters..

<img width="543" alt="image" src="https://user-images.githubusercontent.com/6988/128139832-ef9c5291-f3d7-4402-8625-b45d26b4e5bc.png">
