Handle non-string errors for ES 2+ support

goes.go

@@ -516,6 +516,13 @@ func (c *Client) Do(r Requester) (*Response, error) {
 		}
 	}
 
+	if len(esResp.RawError) > 0 && esResp.RawError[0] == '"' {
+		json.Unmarshal(esResp.RawError, &esResp.Error)
+	} else {
+		esResp.Error = string(esResp.RawError)
+	}
+	esResp.RawError = nil
+
 	if esResp.Error != "" {
 		return esResp, &SearchError{esResp.Error, esResp.Status}
 	}

structs.go

@@ -4,7 +4,10 @@
 
 package goes
 
-import "net/http"
+import (
+	"encoding/json"
+	"net/http"
+)
 
 // Client represents a connection to elasticsearch
 type Client struct {
@@ -23,6 +26,7 @@ type Client struct {
 type Response struct {
 	Acknowledged bool
 	Error        string
+	RawError     json.RawMessage `json:"error"`
 	Errors       bool
 	Status       uint64
 	Took         uint64