Fixed extra comma issue in upload field accept attr

https://www.joomdev.com/forum/jd-simple-contact-form/6562-type-of-files-accepted-as-an-attachment#30258

layouts/fields/file.php

@@ -34,7 +34,7 @@
 $document->addStyleDeclaration($style);
 ?>
 <div class="custom-file">
-   <input id="<?php echo $field->name; ?>-<?php echo $module->id; ?>" accept="<?php foreach ($allowable as $type) { echo ".".$type.","; } ?>" type="file" name="jdscf[<?php echo $field->name; ?>]" class="custom-file-input" <?php echo implode(' ', $attrs); ?>>
+   <input id="<?php echo $field->name; ?>-<?php echo $module->id; ?>" accept="<?php echo '.' . implode( ',.', $allowable ); ?>" type="file" name="jdscf[<?php echo $field->name; ?>]" class="custom-file-input" <?php echo implode(' ', $attrs); ?>>
    <label class="custom-file-label" for="<?php echo $field->name; ?>-<?php echo $module->id; ?>"><?php echo JText::_('MOD_JDSCF_FILE_LBL'); ?></label>
 </div>