Update rust buildpack again

Author: alexcrichton

.buildpacks

@@ -1,4 +1,4 @@
 https://github.com/rcaught/heroku-buildpack-cmake#e4e2c9e
-https://github.com/alexcrichton/heroku-buildpack-rust#5ae46d5
+https://github.com/alexcrichton/heroku-buildpack-rust#98fda9e
 https://github.com/tonycoco/heroku-buildpack-ember-cli#426b308
 https://github.com/ryandotsmith/nginx-buildpack.git#af813ba