minor spelling/grammar corrections

resources/lang/en/validation.php

@@ -27,7 +27,7 @@ return [
 		"string"  => "The :attribute must be between :min and :max characters.",
 		"array"   => "The :attribute must have between :min and :max items.",
 	],
-	"boolean"              => "The :attribute field must be true or false",
+	"boolean"              => "The :attribute field must be true or false.",
 	"confirmed"            => "The :attribute confirmation does not match.",
 	"date"                 => "The :attribute is not a valid date.",
 	"date_format"          => "The :attribute does not match the format :format.",