[tor-bugs] #25714 [Core Tor/Tor]: switch Travis to using Rust stable

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#25714: switch Travis to using Rust stable
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 Reporter:  catalyst                |          Owner:  catalyst
     Type:  task                    |         Status:  needs_review
 Priority:  Medium                  |      Milestone:  Tor: 0.3.4.x-final
Component:  Core Tor/Tor            |        Version:
 Severity:  Normal                  |     Resolution:
 Keywords:  tor-ci, rust, fast-fix  |  Actual Points:
Parent ID:  #25550                  |         Points:
 Reviewer:                          |        Sponsor:  Sponsor3
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Comment (by isis):

 Replying to [comment:3 nickm]:
 > Backporting seems fine to me: it only affects travis builds, not actual
 stability.
 >
 > Adding isis to cc for a second opinion, but this looks fine to me.

 Backporting sounds good to me; we want our tests testing what we actually
 expect to work. :)

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25714#comment:4>
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