Update livecheck strategies to avoid unnecessary redirections

[samford]

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This updates the page_url variables in the Hackage and Pypi livecheck strategies to avoid unnecessary redirections. The URLs are currently redirecting as follows:

• https://hackage.haskell.org/package/Agda/src -> https://hackage.haskell.org/package/Agda/src/
• https://pypi.org/project/Airshare#files -> https://pypi.org/project/Airshare/

page_url was missing the trailing forward slash in both of these cases. The Pypi page_url also includes the #files fragment but it's the missing forward slash, not the fragment, that causes the redirection.

These strategies currently function fine but #9535 made these redirections more apparent and it's always nice to avoid unnecessary redirections when we can.

[BrewTestBot]

Review period will end on 2020-12-15 at 00:00:00 UTC.

[BrewTestBot]

Review period ended.