encode: Fix key encoding for Map dictionaries

Author: jhermsmeier

lib/encode.js

@@ -111,7 +111,9 @@ encode.dictMap = function (buffers, data) {
   // Sort keys to retain
   for (var key of keys) {
     if (data.get(key) == null) continue
-    encode._encode(buffers, key)
+    Buffer.isBuffer(key)
+      ? encode._encode(buffers, key)
+      : encode.string(buffers, String(key))
     encode._encode(buffers, data.get(key))
   }