Use Bazel mirror to download externals (#17)

diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 7f8ed2b..6351d66 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -18,3 +18,4 @@
 Kristina Chodorow <kchodorow@google.com>
 Philipp Wollermann <philwo@google.com>
 Ulf Adams <ulfjack@google.com>
+Justine Alexandra Roberts Tunney <jart@google.com>
diff --git a/rust/rust.bzl b/rust/rust.bzl
index 4eaa8c5..a9b82ed 100644
--- a/rust/rust.bzl
+++ b/rust/rust.bzl
@@ -746,7 +746,7 @@
 def rust_repositories():
   native.new_http_archive(
       name = "rust_linux_x86_64",
-      url = "https://static.rust-lang.org/dist/rust-1.9.0-x86_64-unknown-linux-gnu.tar.gz",
+      url = "http://bazel-mirror.storage.googleapis.com/static.rust-lang.org/dist/rust-1.9.0-x86_64-unknown-linux-gnu.tar.gz",
       strip_prefix = "rust-1.9.0-x86_64-unknown-linux-gnu",
       sha256 = "288ff13efa2577e81c77fc2cb6e2b49b1ed0ceab51b4fa12f7efb87039ac49b7",
       build_file_content = RUST_BUILD_FILE,
@@ -754,7 +754,7 @@
 
   native.new_http_archive(
       name = "rust_darwin_x86_64",
-      url = "https://static.rust-lang.org/dist/rust-1.9.0-x86_64-apple-darwin.tar.gz",
+      url = "http://bazel-mirror.storage.googleapis.com/static.rust-lang.org/dist/rust-1.9.0-x86_64-apple-darwin.tar.gz",
       strip_prefix = "rust-1.9.0-x86_64-apple-darwin",
       sha256 = "d59b5509e69c1cace20a57072e3b3ecefdbfd8c7e95657b0ff2ac10aa1dfebe6",
       build_file_content = RUST_BUILD_FILE,