Bump mikey179/vfsstream from 1.6.7 to 1.6.8

Bumps [mikey179/vfsstream](https://github.com/bovigo/vfsStream) from 1.6.7 to 1.6.8.
- [Release notes](https://github.com/bovigo/vfsStream/releases)
- [Changelog](https://github.com/bovigo/vfsStream/blob/v1.6.8/CHANGELOG.md)
- [Commits](https://github.com/bovigo/vfsStream/compare/v1.6.7...v1.6.8)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

composer.lock

@@ -1539,16 +1539,16 @@
         },
         {
             "name": "mikey179/vfsstream",
-            "version": "v1.6.7",
+            "version": "v1.6.8",
             "source": {
                 "type": "git",
                 "url": "https://github.com/bovigo/vfsStream.git",
-                "reference": "2b544ac3a21bcc4dde5d90c4ae8d06f4319055fb"
+                "reference": "231c73783ebb7dd9ec77916c10037eff5a2b6efe"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/bovigo/vfsStream/zipball/2b544ac3a21bcc4dde5d90c4ae8d06f4319055fb",
-                "reference": "2b544ac3a21bcc4dde5d90c4ae8d06f4319055fb",
+                "url": "https://api.github.com/repos/bovigo/vfsStream/zipball/231c73783ebb7dd9ec77916c10037eff5a2b6efe",
+                "reference": "231c73783ebb7dd9ec77916c10037eff5a2b6efe",
                 "shasum": ""
             },
             "require": {
@@ -1581,7 +1581,7 @@
             ],
             "description": "Virtual file system to mock the real file system in unit tests.",
             "homepage": "http://vfs.bovigo.org/",
-            "time": "2019-08-01T01:38:37+00:00"
+            "time": "2019-10-30T15:31:00+00:00"
         },
         {
             "name": "phar-io/manifest",