Adopt new logo (dmlc#10270)

Author: hcho3

README.md

@@ -1,5 +1,6 @@
-<img src="https://xgboost.ai/images/logo/xgboost-logo.svg" width=135/>  eXtreme Gradient Boosting
+<img src="https://xgboost.ai/images/logo/xgboost-logo-ng-trimmed.png" width=200/> eXtreme Gradient Boosting
 ===========
+
 [![Build Status](https://badge.buildkite.com/aca47f40a32735c00a8550540c5eeff6a4c1d246a580cae9b0.svg?branch=master)](https://buildkite.com/xgboost/xgboost-ci)
 [![XGBoost-CI](https://github.com/dmlc/xgboost/workflows/XGBoost-CI/badge.svg?branch=master)](https://github.com/dmlc/xgboost/actions)
 [![Documentation Status](https://readthedocs.org/projects/xgboost/badge/?version=latest)](https://xgboost.readthedocs.org)

doc/conf.py

@@ -250,7 +250,7 @@ def is_readthedocs_build():
 html_theme_options = {"logo_only": True}
 
 
-html_logo = "https://raw.githubusercontent.com/dmlc/dmlc.github.io/master/img/logo-m/xgboost.png"
+html_logo = "https://xgboost.ai/images/logo/xgboost-logo-ng.png"
 
 html_css_files = ["css/custom.css"]