Update jruby to 9.1.17 and asciidoctorj to v1.5.7

Since Bazel 0.16, the build is done with an embedded JRE using Java
version 9. This causes "illegal reflective access operation" warnings
during the documentation build, because the version of jruby (9.1.13)
doesn't support Java 9.

Support for Java 9 was added in jruby 9.1.14 [1]. The subsequent
releases also include bug fixes (see [2], [3], [4]).

Note that we don't upgrade to the latest (9.2.0).

Also upgrade asciidoctorj to the latest release, 1.5.7.

[1] http://jruby.org/2017/11/08/jruby-9-1-14-0.html
[2] http://jruby.org/2017/12/07/jruby-9-1-15-0.html
[3] http://jruby.org/2018/02/21/jruby-9-1-16-0.html
[4] http://jruby.org/2018/04/23/jruby-9-1-17-0.html

Bug: Issue 9766
Change-Id: I2f84612905761c4bdfddca807e92f54247ef6f6e

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index 3d477f2..e4bc3b4 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -863,14 +863,14 @@
 
 maven_jar(
     name = "asciidoctor",
-    artifact = "org.asciidoctor:asciidoctorj:1.5.6",
-    sha1 = "bb757d4b8b0f8438ce2ed781f6688cc6c01d9237",
+    artifact = "org.asciidoctor:asciidoctorj:1.5.7",
+    sha1 = "8e8c1d8fc6144405700dd8df3b177f2801ac5987",
 )
 
 maven_jar(
     name = "jruby",
-    artifact = "org.jruby:jruby-complete:9.1.13.0",
-    sha1 = "8903bf42272062e87a7cbc1d98919e0729a9939f",
+    artifact = "org.jruby:jruby-complete:9.1.17.0",
+    sha1 = "76716d529710fc03d1d429b43e3cedd4419f78d4",
 )
 
 maven_jar(