Bump depot_tools version

ignisf · ignisf · commit 18044d556d4b · 2017-12-05T11:01:55.000+02:00
diff --git a/vendor/depot_tools b/vendor/depot_tools
@@ -1 +1 @@
-Subproject commit 83fd81f8a4eef6c8f176a7257662b18cac3e89be
+Subproject commit b278ddd9392390c5136079638f7fadb0d6c55f6b
