Colors in cacheFileReport cannot be switched of

I am using

```
vendor/bin/phpcs --report="diff" --extensions="php" --no-colors --report-diff=var/phpcs_report_680bb28374ffe.diff
```

to see some progress. In this case, it was not possible to switch of colors in the diff file.

Author: amenk

src/Reporter.php

@@ -290,6 +290,10 @@ public function cacheFileReport(File $phpcsFile)
             $generatedReport = ob_get_contents();
             ob_end_clean();
 
+            if ($this->config->colors !== true) {
+                $generatedReport = Common::stripColors($generatedReport);
+            }
+
             if ($report['output'] === null) {
                 // Using a temp file.
                 if (isset($this->tmpFiles[$type]) === false) {