Fix plugin builds on OSX

This fixes plugin stamping by adding overwrite files without
prompting option to unzip command.

Inspired-by: David Ostrovsky <david@ostrovsky.org>
Issue: 13105
Change-Id: Ifb0dac4987d85f57333f27f9602a873ecb5440e9
diff --git a/tools/bzl/plugin.bzl b/tools/bzl/plugin.bzl
index 92f9309..5ef8229 100644
--- a/tools/bzl/plugin.bzl
+++ b/tools/bzl/plugin.bzl
@@ -106,7 +106,7 @@
             "export TZ",
             "GEN_VERSION=$$(cat bazel-out/stable-status.txt | grep -w STABLE_BUILD_%s_LABEL | cut -d ' ' -f 2)" % dir_name.upper(),
             "cd $$TMP",
-            "unzip -q $$ROOT/$<",
+            "unzip -qo $$ROOT/$<",
             "echo \"Implementation-Version: $$GEN_VERSION\n$$(cat META-INF/MANIFEST.MF)\" > META-INF/MANIFEST.MF",
             "find . -exec touch '{}' ';'",
             "zip -Xqr $$ROOT/$@ .",