Fix Test:Unit to display in Unit view with version 3.16 or newer.

Auto runner registration has been made lazy upstream so it was printing
on console only.
Fix is to require test/unit eagerly in DLTK runner.
See
https://github.com/test-unit/test-unit/commit/6f539cb0e64140bbe1fbfa0e6a18532b0587f422
for details.

Change-Id: I003fa810af5184f6eac269b8749aaac67e452e00
Signed-off-by: Alexander Kurtakov <akurtako@redhat.com>
diff --git a/plugins/org.eclipse.dltk.ruby.testing/testing/dltk-testunit-runner.rb b/plugins/org.eclipse.dltk.ruby.testing/testing/dltk-testunit-runner.rb
index ce6363a..c229c55 100644
--- a/plugins/org.eclipse.dltk.ruby.testing/testing/dltk-testunit-runner.rb
+++ b/plugins/org.eclipse.dltk.ruby.testing/testing/dltk-testunit-runner.rb
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2008 xored software, Inc. and others
+# Copyright (c) 2008, 2016 xored software, Inc. and others
 # All rights reserved. This program and the accompanying materials
 # are made available under the terms of the Eclipse Public License v1.0
 # which accompanies this distribution, and is available at
@@ -8,7 +8,7 @@
 # Contributors:
 #    xored software, Inc. - initial API and Implementation (Alex Panchenko)
 #
-
+require 'test/unit'
 require 'test/unit/ui/console/testrunner'
 require 'socket'