Auto merge of #18942 - servo:static.rlo, r=jdm,mbrubeck

Bootstrap from more permanent URLs

The `rust-lang-ci` S3 bucket is ephemeral. `static-rust-lang-org.s3.amazonaws.com` is not going away soon, but using `static.rust-lang.org` when possible keeps things working if it ever does.

https://internals.rust-lang.org/t/updates-on-rusts-ci-uploads/6062
https://internals.rust-lang.org/t/public-stable-rust-services/6072

We’ll still need to find a solution for "alt" rustc builds. In the meantime, this is a step.

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python/requirements.txt

@@ -26,4 +26,9 @@ colorama == 0.3.7
 # For package uploading
 boto3 == 1.4.4
 
+# Default root CAs on Windows CI do not trust CloudFront certificates,
+# connecting to https://static.rust-lang.org would fail:
+# https://github.com/servo/servo/pull/18942
+certifi
+
 -e python/tidy