Adjusts URL detection to be case insensitive

Per [RFC 3986](https://tools.ietf.org/html/rfc3986#section-3.1), the URL schema (e.g., http:, https:) should be case insensitive. This PR adjusts the URL detection regex to ensure that capitalized schemas (e.g., HTTP, HTTPS) are supported.

src/wsdl/index.ts

@@ -1169,7 +1169,7 @@ export class WSDL {
     }
 
     let includePath: string;
-    if (!/^https?:/.test(this.uri) && !/^https?:/.test(include.location)) {
+    if (!/^https?:/i.test(this.uri) && !/^https?:/i.test(include.location)) {
       includePath = path.resolve(path.dirname(this.uri), include.location);
     } else {
       includePath = url.resolve(this.uri || '', include.location);