downgrade to kirby v3

kirby/config/fields/text.php

@@ -10,7 +10,7 @@ return [
 		 * The field value will be converted with the selected converter before the value gets saved. Available converters: `lower`, `upper`, `ucfirst`, `slug`
 		 */
 		'converter' => function ($value = null) {
-			if ($value !== null && array_key_exists($value, $this->converters()) === false) {
+			if ($value !== null && in_array($value, array_keys($this->converters())) === false) {
 				throw new InvalidArgumentException([
 					'key'  => 'field.converter.invalid',
 					'data' => ['converter' => $value]
@@ -27,13 +27,6 @@ return [
 			return $counter;
 		},
 
-		/**
-		 * Sets the font family (sans or monospace)
-		 */
-		'font' => function (string $font = null) {
-			return $font === 'monospace' ? 'monospace' : 'sans-serif';
-		},
-
 		/**
 		 * Maximum number of allowed characters
 		 */