Bug fix: loadInstalledPaths() very very broken since PHPCS 3.1.0

The PHPCS `--config-show` command shows **all** config settings set, not just the `installed_paths` and since PHPCS 3.1.0, it also includes a line to indicate which configuration file is being used to help with debugging configuration issues.

In PHPCS 2.0 - 3.0.1, if any [other configuration options](https://github.com/squizlabs/PHP_CodeSniffer/wiki/Configuration-Options) were set, the result of the `loadInstalledPaths()` command would be broken.

In PHPCS 3.1.0+, the result would always be broken, no matter what.

In effect this means that the `installed_paths` would (nearly) always be set as if the config was previously non-existent as the `cleanInstalledPaths()` method would empty out the array as the values contained therein would be invalid anyway.

It would be lovely if it were possible to add unit tests, but as we're talking about a `private` method setting a `private` property...

So, for now, to proof the bug and validate the fix, I've set up a "fake" unit test to demonstrate what the previous behaviour was and what the behaviour will be with this fix in place: https://3v4l.org/XKMIf

src/Plugin.php

@@ -46,6 +46,7 @@ class Plugin implements PluginInterface, EventSubscriberInterface
     const PACKAGE_NAME = 'squizlabs/php_codesniffer';
     const PACKAGE_TYPE = 'phpcodesniffer-standard';
 
+    const PHPCS_CONFIG_REGEX = '`%s:[^\r\n]+`';
     const PHPCS_CONFIG_KEY = 'installed_paths';
 
     /**
@@ -199,22 +200,29 @@ public function onDependenciesChangedEvent()
      */
     private function loadInstalledPaths()
     {
-        if ($this->isPHPCodeSnifferInstalled() === true) {
-            $this->processExecutor->execute(
-                sprintf(
-                    'phpcs --config-show %s',
-                    self::PHPCS_CONFIG_KEY
-                ),
-                $output,
-                $this->composer->getConfig()->get('bin-dir')
-            );
+        if ($this->isPHPCodeSnifferInstalled() !== true) {
+            return;
+        }
+
+        $this->processExecutor->execute(
+            sprintf(
+                'phpcs --config-show %s',
+                self::PHPCS_CONFIG_KEY
+            ),
+            $output,
+            $this->composer->getConfig()->get('bin-dir')
+        );
 
-            $phpcsInstalledPaths = str_replace(self::PHPCS_CONFIG_KEY . ': ', '', $output);
-            $phpcsInstalledPaths = trim($phpcsInstalledPaths);
+        $regex = sprintf(self::PHPCS_CONFIG_REGEX, self::PHPCS_CONFIG_KEY);
+        if (preg_match($regex, $output, $match) !== 1) {
+            return;
+        }
 
-            if ($phpcsInstalledPaths !== '') {
-                $this->installedPaths = explode(',', $phpcsInstalledPaths);
-            }
+        $phpcsInstalledPaths = str_replace(self::PHPCS_CONFIG_KEY . ': ', '', $match[0]);
+        $phpcsInstalledPaths = trim($phpcsInstalledPaths);
+
+        if ($phpcsInstalledPaths !== '') {
+            $this->installedPaths = explode(',', $phpcsInstalledPaths);
         }
     }