lib: constants: change CHROMITE_BIN_DIR to Path

BUG=None
TEST=CQ passes

Change-Id: Id3885f232af7a700f33183164b43d1da4295145f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4374329
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index eedf978..d49bdf1 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -32,7 +32,7 @@
     import portage
 
 
-EMERGE_CMD = os.path.join(constants.CHROMITE_BIN_DIR, "parallel_emerge")
+EMERGE_CMD = constants.CHROMITE_BIN_DIR / "parallel_emerge"
 PACKAGE_STABLE = "[stable]"
 
 CHROMIUMOS_OVERLAY = os.path.join(