Changed to constructor functions

validators/boolean.ts

@@ -1,14 +1,16 @@
 import { Validator, Args } from "../mod.ts";
 
-export const isBoolean: Validator = {
-  type: "isBoolean",
-  check: (value: any) => {
-    if (value === null || value === undefined) return;
-    if (value !== true && value !== false) {
-      return {};
-    }
-  },
-  message: (value: any, args?: Args) => {
-    return `This value has to be a boolean.`;
-  },
-};
+export function isBoolean(): Validator {
+  return {
+    type: "isBoolean",
+    check: (value: any) => {
+      if (value === null || value === undefined) return;
+      if (value !== true && value !== false) {
+        return {};
+      }
+    },
+    message: (value: any, args?: Args) => {
+      return `This value has to be a boolean.`;
+    },
+  };
+}