Update latest bazel version to 0.20.0. (#256)

container/build.py

diff --git a/container/build.py b/container/build.py
index 662b62b..aaf3912 100644
--- a/container/build.py
+++ b/container/build.py
@@ -80,7 +80,7 @@
 import subprocess
 import sys
 
-LATEST_BAZEL_VERSION = "0.19.2"
+LATEST_BAZEL_VERSION = "0.20.0"
 
 SUPPORTED_TYPES = [
     "rbe-debian8", "rbe-ubuntu16_04", "ubuntu16_04-bazel",

container/common/bazel/version.bzl

diff --git a/container/common/bazel/version.bzl b/container/common/bazel/version.bzl
index 3a419d7..04efc7d 100644
--- a/container/common/bazel/version.bzl
+++ b/container/common/bazel/version.bzl
@@ -9,4 +9,5 @@
     "0.18.1": "8073657ced2bb323dd2e7ba6e39011ca56b856cae475b476e9b77d30123582e5",
     "0.19.0": "b9e988643b10444d6d8eb04461418b7b80e3d171e12d1c8b6e2a50f541e739e7",
     "0.19.2": "42ba631103011594cdf5591ef07658a9e9a5d73c5ee98a9f09651ac4ac535d8c",
+    "0.20.0": "44aed3bd8e58a889ee36f187a4b1cb573a2b4cc7a3d7c0cf0696205764e45dec",
 }