Update six.BUILD

third_party/six.BUILD

 load("@rules_python//python:defs.bzl", "py_library")
 
+# Consume `six.py` as `__init__.py` for compatibility
+# with `--incompatible_default_to_explicit_init_py`.
+# https://github.com/protocolbuffers/protobuf/pull/6795#issuecomment-546060749
+# https://github.com/bazelbuild/bazel/issues/10076
+genrule(
+  name = "copy_six",
+  srcs = ["six-1.12.0/six.py"],
+  outs = ["__init__.py"],
+  cmd = "cp $< $(@)",
+)
+
 py_library(
-    name = "six",
-    srcs = ["six.py"],
-    srcs_version = "PY2AND3",
-    visibility = ["//visibility:public"],
+  name = "six",
+  srcs = ["__init__.py"],
+  srcs_version = "PY2AND3",
+  visibility = ["//visibility:public"],
 )