fix GH Action badge in readme (#153)

Author: agramfort

.github/workflows/pythonpackage.yml

@@ -1,4 +1,4 @@
-name: Test Package
+name: build
 
 on:
   push:

README.md

@@ -3,7 +3,7 @@
 [![PyPI version](https://badge.fury.io/py/POT.svg)](https://badge.fury.io/py/POT)
 [![Anaconda Cloud](https://anaconda.org/conda-forge/pot/badges/version.svg)](https://anaconda.org/conda-forge/pot)
 [![Build Status](https://travis-ci.org/PythonOT/POT.svg?branch=master)](https://travis-ci.org/PythonOT/POT)
-[![Build Status](https://github.com/PythonOT/POT/workflows/Linux%7CWin%7CMacOS/badge.svg)](https://github.com/PythonOT/POT/actions)
+[![Build Status](https://github.com/PythonOT/POT/workflows/build/badge.svg)](https://github.com/PythonOT/POT/actions)
 [![Codecov Status](https://codecov.io/gh/PythonOT/POT/branch/master/graph/badge.svg)](https://codecov.io/gh/PythonOT/POT)
 [![Downloads](https://pepy.tech/badge/pot)](https://pepy.tech/project/pot)
 [![Anaconda downloads](https://anaconda.org/conda-forge/pot/badges/downloads.svg)](https://anaconda.org/conda-forge/pot)