Fix rustfmt installation to be via rustup.

Author: emilio

ci/script.sh

@@ -13,7 +13,7 @@ case "$BINDGEN_JOB" in
     "test")
         # Need rustfmt to compare the test expectations.
         rustup update nightly
-        rustup run nightly cargo install -f rustfmt-nightly
+        rustup component add rustfmt
 
         cargo test $BINDGEN_PROFILE --features "$BINDGEN_FEATURES"
         ./ci/assert-no-diff.sh