migrate to "export default"

also, set no-use-before-define in linter

src/dig.js

@@ -13,10 +13,6 @@ function resolveWrapper(hostname, rrtype, options) {
     return resolve(hostname, rrtype, options);
 }
 
-export {
-    resolveWrapper as resolve,
-    _setMockResolve,
-};
 
 // a note on TXT records. It doesn't have quotes ("") at the DNS level. Those quotes
 // are added for DNS server software to enclose spaces. Such quotes may also be returned
@@ -36,3 +32,8 @@ async function resolve(hostname, rrtype, options) {
     // we sometimes get empty array and sometimes ENODATA. for TXT records, result is 2d array of strings
     return result;
 }
+
+export default {
+    resolve: resolveWrapper,
+    _setMockResolve,
+};