[Website] Fix download links on website for tarballs, checksums

[asfimport]

See discussion on the ANNOUNCE thread for 0.10.0

Reporter: Wes McKinney / @wesm
Assignee: Krisztian Szucs / @kszucs

PRs and other links:

• GitHub Pull Request #2613

_{Note: This issue was originally created as ARROW-3013. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 2613
#2613