Update go-ucfg to 0.6.1 (#7599)

Update fixes config unpacking if users overwrite settings from CLI, with
missing values. When using `-E key=` (e.g. in scripts defining potential
empty defaults via env variables like `-E key=${MYVALUE}`), an untyped
`nil`-values was inserted into the config. This untyped value will make
Unpack fail for most typed settings.

CHANGELOG.asciidoc

@@ -79,6 +79,7 @@ https://github.com/elastic/beats/compare/v6.2.3...master[Check the HEAD diff]
 - Fix default value for logging.files.keepfiles. It was being set to 0 and now
   it's set to the documented value of 7. {issue}7494[7494]
 - Retain compatibility with older Docker server versions. {issue}7542[7542]
+- Fix errors unpacking configs modified via CLI by ignoring `-E key=value` pairs with missing value. {pull}7599[7599]
 
 *Auditbeat*
 

NOTICE.txt

@@ -446,8 +446,8 @@ Apache License 2.0
 
 --------------------------------------------------------------------
 Dependency: github.com/elastic/go-ucfg
-Version: v0.6.0
-Revision: 9c66f5c432b1d25bdb449a1e588d58b5d0cd7268
+Version: v0.6.1
+Revision: 581f7b1fe9d84f4c18ef0694d6e0eb944a925dae
 License type (autodetected): Apache-2.0
 ./vendor/github.com/elastic/go-ucfg/LICENSE:
 --------------------------------------------------------------------

vendor/vendor.json

@@ -623,52 +623,52 @@
 			"versionExact": "v0.0.1"
 		},
 		{
-			"checksumSHA1": "d0qibYdQy5G1YqI5H+xNC0QJ66g=",
+			"checksumSHA1": "MK8/w0Idj7kRBUiBabARPdm9hOo=",
 			"path": "github.com/elastic/go-ucfg",
-			"revision": "9c66f5c432b1d25bdb449a1e588d58b5d0cd7268",
-			"revisionTime": "2018-07-04T14:42:58Z",
-			"version": "v0.6.0",
-			"versionExact": "v0.6.0"
+			"revision": "581f7b1fe9d84f4c18ef0694d6e0eb944a925dae",
+			"revisionTime": "2018-07-13T14:04:29Z",
+			"version": "v0.6.1",
+			"versionExact": "v0.6.1"
 		},
 		{
 			"checksumSHA1": "X+R/CD8SokJrmlxFTx2nSevRDhQ=",
 			"path": "github.com/elastic/go-ucfg/cfgutil",
-			"revision": "9c66f5c432b1d25bdb449a1e588d58b5d0cd7268",
-			"revisionTime": "2018-07-04T14:42:58Z",
-			"version": "v0.6.0",
-			"versionExact": "v0.6.0"
+			"revision": "581f7b1fe9d84f4c18ef0694d6e0eb944a925dae",
+			"revisionTime": "2018-07-13T14:04:29Z",
+			"version": "v0.6.1",
+			"versionExact": "v0.6.1"
 		},
 		{
-			"checksumSHA1": "dShGF53hLUufO70RAjju+RT0fHY=",
+			"checksumSHA1": "zC8mCPW/pPPNcuHQOc/B/Ej1W1U=",
 			"path": "github.com/elastic/go-ucfg/flag",
-			"revision": "9c66f5c432b1d25bdb449a1e588d58b5d0cd7268",
-			"revisionTime": "2018-07-04T14:42:58Z",
-			"version": "v0.6.0",
-			"versionExact": "v0.6.0"
+			"revision": "581f7b1fe9d84f4c18ef0694d6e0eb944a925dae",
+			"revisionTime": "2018-07-13T14:04:29Z",
+			"version": "v0.6.1",
+			"versionExact": "v0.6.1"
 		},
 		{
 			"checksumSHA1": "esXpiQlEvTOUwsE0nNesso8albo=",
 			"path": "github.com/elastic/go-ucfg/internal/parse",
-			"revision": "9c66f5c432b1d25bdb449a1e588d58b5d0cd7268",
-			"revisionTime": "2018-07-04T14:42:58Z",
-			"version": "v0.6.0",
-			"versionExact": "v0.6.0"
+			"revision": "581f7b1fe9d84f4c18ef0694d6e0eb944a925dae",
+			"revisionTime": "2018-07-13T14:04:29Z",
+			"version": "v0.6.1",
+			"versionExact": "v0.6.1"
 		},
 		{
 			"checksumSHA1": "5mXUhhlPdvcAFKiQENInTJWrtQM=",
 			"path": "github.com/elastic/go-ucfg/json",
-			"revision": "9c66f5c432b1d25bdb449a1e588d58b5d0cd7268",
-			"revisionTime": "2018-07-04T14:42:58Z",
-			"version": "v0.6.0",
-			"versionExact": "v0.6.0"
+			"revision": "581f7b1fe9d84f4c18ef0694d6e0eb944a925dae",
+			"revisionTime": "2018-07-13T14:04:29Z",
+			"version": "v0.6.1",
+			"versionExact": "v0.6.1"
 		},
 		{
 			"checksumSHA1": "Bg6vistPQLftv2fEYB7GWwSExv8=",
 			"path": "github.com/elastic/go-ucfg/yaml",
-			"revision": "9c66f5c432b1d25bdb449a1e588d58b5d0cd7268",
-			"revisionTime": "2018-07-04T14:42:58Z",
-			"version": "v0.6.0",
-			"versionExact": "v0.6.0"
+			"revision": "581f7b1fe9d84f4c18ef0694d6e0eb944a925dae",
+			"revisionTime": "2018-07-13T14:04:29Z",
+			"version": "v0.6.1",
+			"versionExact": "v0.6.1"
 		},
 		{
 			"checksumSHA1": "yu/X+qHftvfQlAnjPdYLwrDn2nI=",