Update bazel WORKSPACE

This abseil update fixes some warnings with newer versions of clang and
gcc, and now requires bazel_skylib.

Change-Id: I3a30dda252260a2950a6bb46975840b627cc2d8a

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 809e6b9..e8a43ca 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -5,9 +5,23 @@
 workspace(name = "com_google_googleurl")
 
 load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "bazel_skylib",
+    sha256 = "74d544d96f4a5bb630d465ca8bbcfe231e3594e5aae57e1edbf17a6eb3ca2506",
+    urls = [
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.3.0/bazel-skylib-1.3.0.tar.gz",
+        "https://github.com/bazelbuild/bazel-skylib/releases/download/1.3.0/bazel-skylib-1.3.0.tar.gz",
+    ],
+)
+
+load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
+
+bazel_skylib_workspace()
 
 git_repository(
     name = "com_google_absl",
-    commit = "17c954d90d5661e27db8fc5f086085690a8372d9",
+    commit = "c814d4e28b65bb4c492b4d897105971de85c1b6e",
     remote = "https://github.com/abseil/abseil-cpp.git",
 )