chore(internal): update isAbsoluteURL (#531)

Author: stainless-app[bot]

src/core.ts

@@ -951,8 +951,8 @@ export const safeJSON = (text: string) => {
   }
 };
 
-// https://stackoverflow.com/a/19709846
-const startsWithSchemeRegexp = new RegExp('^(?:[a-z]+:)?//', 'i');
+// https://url.spec.whatwg.org/#url-scheme-string
+const startsWithSchemeRegexp = /^[a-z][a-z0-9+.-]*:/i;
 const isAbsoluteURL = (url: string): boolean => {
   return startsWithSchemeRegexp.test(url);
 };