Enabled experimental_multi_threaded_digest

This should speed up MD5summing results significantly

Change-Id: Ic4d19c7e9864ca376960780f0237154ca9b6cc2e
diff --git a/tools/bazel.rc b/tools/bazel.rc
index c8d93d0..0e3001f 100644
--- a/tools/bazel.rc
+++ b/tools/bazel.rc
@@ -53,3 +53,4 @@
 test --test_output=errors
 
 build --experimental_sandbox_shm
+build --experimental_multi_threaded_digest