Bump TF Linux RBE toolchains

https://github.com/tensorflow/toolchains/releases/tag/v1.3.7
https://github.com/tensorflow/toolchains/releases/tag/v1.3.8

PiperOrigin-RevId: 423595424
Change-Id: Ia00affbc63f91673a0c7a521c0067ca226e8c764
diff --git a/tensorflow/workspace3.bzl b/tensorflow/workspace3.bzl
index 26b132e..5db1e26 100644
--- a/tensorflow/workspace3.bzl
+++ b/tensorflow/workspace3.bzl
@@ -17,11 +17,11 @@
 
     http_archive(
         name = "tf_toolchains",
-        sha256 = "28528dc62e0e3b5e565e1fe49ec01b8ebae49c985a0ab798fce7f85c862f5ef9",
-        strip_prefix = "toolchains-1.3.6",
+        sha256 = "4aed43f3fdf0fef53a4ceb10d215f8958dd4b2f1d043ede12dbdd5f2c37fa14f",
+        strip_prefix = "toolchains-1.3.8",
         urls = [
-            "http://mirror.tensorflow.org/github.com/tensorflow/toolchains/archive/v1.3.6.tar.gz",
-            "https://github.com/tensorflow/toolchains/archive/v1.3.6.tar.gz",
+            "http://mirror.tensorflow.org/github.com/tensorflow/toolchains/archive/v1.3.8.tar.gz",
+            "https://github.com/tensorflow/toolchains/archive/v1.3.8.tar.gz",
         ],
     )