bug #1231 PHP7.4 deprecates first implode parameter being pieces, sec…

…ond glue (wimg)

This PR was merged into the 6.2-dev branch.

Discussion
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PHP7.4 deprecates first implode parameter being pieces, second glue

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Doc update?   | no
| BC breaks?    | no
| Deprecations? | yes
| Fixed tickets |
| License       | MIT

PHP 7.4 deprecates in the implode function the use of the 'pieces' parameter as the first parameter and the 'glue' parameter as the second parameter.

Commits
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702a9d7 PHP7.4 deprecates first implode parameter being pieces, second glue

lib/swiftmailer_generate_mimes_config.php

@@ -173,7 +173,7 @@ function generateUpToDateMimeArray()
     ksort($valid_mime_types);
 
     // combine mime types and extensions array
-    $output = "$preamble\$swift_mime_types = array(\n    ".implode($valid_mime_types, ",\n    ")."\n);";
+    $output = "$preamble\$swift_mime_types = array(\n    ".implode(",\n    ", $valid_mime_types)."\n);";
 
     // write mime_types.php config file
     @file_put_contents('./mime_types.php', $output);