fix lint warnings

classes/headers.js

@@ -0,0 +1,27 @@
+class Headers {
+  constructor(rawHeaders) {
+    this.rawHeaders = rawHeaders;
+  }
+
+  entries() {
+    return Object.entries(this.rawHeaders);
+  }
+
+  keys() {
+    return Object.keys(this.rawHeaders);
+  }
+
+  values() {
+    return Object.values(this.rawHeaders);
+  }
+
+  get(name) {
+    return this.rawHeaders[name.toLowerCase()] || null;
+  }
+
+  has(name) {
+    return !!this.get(name);
+  }
+}
+
+module.exports = Headers;