normalize response header getters

Author: daltonpearson

lib/browser/FetchHttpStack.ts

@@ -93,7 +93,7 @@ class FetchResponse implements HttpResponse {
   }
 
   getHeader(header: string): string | undefined {
-    return this._res.headers.get(header) || undefined
+    return this._res.headers.get(header) || this._res.headers.get(header.toLowerCase()) || undefined
   }
 
   getBody(): string {

lib/browser/XHRHttpStack.ts

@@ -112,7 +112,11 @@ class XHRResponse implements HttpResponse {
   }
 
   getHeader(header: string): string | undefined {
-    return this._xhr.getResponseHeader(header) || undefined
+    return (
+      this._xhr.getResponseHeader(header) ||
+      this._xhr.getResponseHeader(header.toLowerCase()) ||
+      undefined
+    )
   }
 
   getBody(): string {

test/spec/helpers/utils.js

@@ -184,7 +184,9 @@ export class TestResponse {
   }
 
   getHeader(header) {
-    return this._response.responseHeaders[header]
+    return (
+      this._response.responseHeaders[header] || this._response.responseHeaders[header.toLowerCase()]
+    )
   }
 
   getBody() {