refactor: improve type safety and code style

src/builders/index.ts

@@ -11,7 +11,7 @@ export interface IBuilder<T> {
 
 export class Builder {
     public static getEnv(env: Env): IBuilder<Env> {
-        let b = new EnvBuilder();
+        const b = new EnvBuilder();
         b.src = env;
         return b;
     };