Update //third_party/protobuf to version 3.

third_party/protobuf/ruby/travis-test.sh

+#!/usr/bin/env bash
+
+# Exit on any error.
+set -e
+
+test_version() {
+  version=$1
+  if [ "$version" == "jruby" ] ; then
+    # No conformance tests yet -- JRuby is too broken to run them.
+    bash --login -c \
+      "rvm install $version && rvm use $version && \
+       which ruby && \
+       gem install bundler && bundle && \
+       rake test"
+  else
+    bash --login -c \
+      "rvm install $version && rvm use $version && \
+       which ruby && \
+       gem install bundler && bundle && \
+       rake test"
+    # TODO(xiaofeng): Conformance tests are disabled because the ruby testee
+    # program crashes on some inputs.
+    #  cd ../conformance && \
+    #  make test_ruby
+  fi
+}
+
+test_version $1