修改了部分接口字符串拼接的模式，从 + 改为StringBuffer

Author: tianmu

weixin-java-mp/src/main/java/me/chanjar/weixin/mp/api/WxMpConfigStorage.java

@@ -69,9 +69,9 @@ public interface WxMpConfigStorage {
 
   public String getSecret();
 
-    public String getPartnerId();
-
-    public String getPartnerKey();
+  public String getPartnerId();
+  
+  public String getPartnerKey();
 
   public String getToken();