Update rules_docker. (#278)

diff --git a/repositories/repositories.bzl b/repositories/repositories.bzl
index b153356..ebb0d7c 100644
--- a/repositories/repositories.bzl
+++ b/repositories/repositories.bzl
@@ -56,9 +56,9 @@
     if "io_bazel_rules_docker" not in excludes:
         http_archive(
             name = "io_bazel_rules_docker",
-            sha256 = "aed1c249d4ec8f703edddf35cbe9dfaca0b5f5ea6e4cd9e83e99f3b0d1136c3d",
-            strip_prefix = "rules_docker-0.7.0",
-            urls = ["https://github.com/bazelbuild/rules_docker/archive/v0.7.0.tar.gz"],
+            sha256 = "4abb48f56b838957c9c72ac511b44f79612fcf39d08338fad14a8e3f6b0572ea",
+            strip_prefix = "rules_docker-b8ff6a85ec359db3fd5657accd3e524daf12016d",
+            urls = ["https://github.com/bazelbuild/rules_docker/archive/b8ff6a85ec359db3fd5657accd3e524daf12016d.tar.gz"],
         )
 
         # Register the docker toolchain type