Fix various memory leaks under Windows (elastic#12100)

A function in go-sysinfo used under Windows to split a command-line into arguments was leaking memory.

This code was used in various places:

add_process_metadata processor. (enabled by default in all Beats)
Packetbeat's process monitor. (disabled by default).
Auditbeat's system/process metricset.
This PR updates vendored go-sysinfo to the most recent version, which fixes the leak.

(cherry picked from commit a5b3f0a)

CHANGELOG.next.asciidoc

@@ -33,9 +33,12 @@ https://github.com/elastic/beats/compare/v6.7.2...6.8[Check the HEAD diff]
 
 *Affecting all Beats*
 
+- Fixed a memory leak when using the add_process_metadata processor under Windows. {pull}12100[12100]
+
 *Auditbeat*
 
 - Package dataset: Log error when Homebrew is not installed. {pull}11667[11667]
+- Process dataset: Fixed a memory leak under Windows. {pull}12100[12100]
 
 *Filebeat*
 
@@ -50,6 +53,8 @@ https://github.com/elastic/beats/compare/v6.7.2...6.8[Check the HEAD diff]
 
 *Packetbeat*
 
+- Fixed a memory leak when using process monitoring under Windows. {pull}12100[12100]
+
 *Winlogbeat*
 
 *Functionbeat*

NOTICE.txt

@@ -541,15 +541,15 @@ Apache License 2.0
 
 --------------------------------------------------------------------
 Dependency: github.com/elastic/go-sysinfo
-Revision: ab4f04edfc3d6b3864f5f06a068ddab9ad79774f
+Revision: 9a4be54a53be4c48b44d351d52fb425a5e274be5
 License type (autodetected): Apache-2.0
 ./vendor/github.com/elastic/go-sysinfo/LICENSE.txt:
 --------------------------------------------------------------------
 Apache License 2.0
 
 -------NOTICE.txt-----
 Elastic go-sysinfo
-Copyright 2017-2018 Elasticsearch B.V.
+Copyright 2017-2019 Elasticsearch B.V.
 
 This product includes software developed at
 Elasticsearch, B.V. (https://www.elastic.co/).