Updated application/json Content-Type header detect to allow detectin…

…g application/json when length is longer than 16 character because of addition encoding in the header value, aka 'Content-type: application/json; charset=utf-8'

plugins/in_http/http_prot.c

@@ -523,7 +523,7 @@ static int process_payload(struct flb_http *ctx, struct http_conn *conn,
         return -1;
     }
 
-    if (header->val.len == 16 &&
+    if (header->val.len >= 16 &&
         strncasecmp(header->val.data, "application/json", 16) == 0) {
         type = HTTP_CONTENT_JSON;
     }