Prepend http:// to http(s)_proxy env if missing (#1439)

* Prepend http:// to http(s)_proxy env if missing

* Formatting

* Fix linting

src/proxy.ts

@@ -14,7 +14,12 @@ export function getProxyUrl(reqUrl: URL): URL | undefined {
   })()
 
   if (proxyVar) {
-    return new URL(proxyVar)
+    try {
+      return new URL(proxyVar)
+    } catch {
+      if (!proxyVar.startsWith('http://') && !proxyVar.startsWith('https://'))
+        return new URL(`http://${proxyVar}`)
+    }
   } else {
     return undefined
   }