Add language line for the "present" validation rule.

resources/lang/en/validation.php

@@ -58,6 +58,7 @@ return [
     'not_in'               => 'The selected :attribute is invalid.',
     'numeric'              => 'The :attribute must be a number.',
     'regex'                => 'The :attribute format is invalid.',
+    'present'              => 'The :attribute field must be present.',
     'required'             => 'The :attribute field is required.',
     'required_if'          => 'The :attribute field is required when :other is :value.',
     'required_unless'      => 'The :attribute field is required unless :other is in :values.',