Roll zlib to 718f686

Bug: chromium:697481
Change-Id: I7ec0feb8f2012f3d17dfa55b2636f7331b400efe
Reviewed-on: https://pdfium-review.googlesource.com/10790
Reviewed-by: Nicolás Peña <npm@chromium.org>
Commit-Queue: Nicolás Peña <npm@chromium.org>
diff --git a/DEPS b/DEPS
index 552783d..50f9b93 100644
--- a/DEPS
+++ b/DEPS
@@ -26,7 +26,7 @@
   'v8_revision': '539f7ab310f8865090c494b0251c45e7c52ae5f5',
   'yasm_binary_revision': '52f9b3f4b0aa06da24ef8b123058bb61ee468881',
   'yasm_source_revision': '7da28c6c7c6a1387217352ce02b31754deb54d2a',
-  'zlib_revision': 'eed2732a73838fd581cb25819ab1c4f478d6b38f',
+  'zlib_revision': '718f686437b89038ac83525f4f1b1888aadd9bfc',
 }
 
 deps = {