Update bazel-toolchains repo to use Bazel 0.6.0 toolchain configs.

PiperOrigin-RevId: 171048721

BUILD

diff --git a/BUILD b/BUILD
index 9d65300..18a338d 100644
--- a/BUILD
+++ b/BUILD
@@ -106,6 +106,6 @@
 # Will be removed once toolchain fetching is supported.
 filegroup(
     name = "dummy_toolchain_reference",
-    srcs = ["@bazel_toolchains//configs/debian8_clang/0.1.0:empty"],
+    srcs = ["@bazel_toolchains//configs/debian8_clang/0.1.0/bazel_0.6.0:empty"],
     visibility = ["//visibility:public"],
 )