Append char instead of String

Author: Stephane Landelle

providers/netty/src/main/java/org/asynchttpclient/providers/netty/request/NettyRequestFactory.java

@@ -189,9 +189,9 @@ private byte[] computeBodyFromParams(List<Param> params, Charset bodyCharset) {
         StringBuilder sb = new StringBuilder();
         for (Param param : params) {
             UTF8UrlEncoder.appendEncoded(sb, param.getName());
-            sb.append("=");
+            sb.append('=');
             UTF8UrlEncoder.appendEncoded(sb, param.getValue());
-            sb.append("&");
+            sb.append('&');
         }
         sb.setLength(sb.length() - 1);
         return sb.toString().getBytes(bodyCharset);