Merge branch '38_binder_gcc' into 'master'

Make Binder work again (at least for C++ 17 kernel)

See merge request formations/cpp/gettingstartedwithmoderncpp!40

environment.yml → binder/environment.yml

@@ -2,7 +2,6 @@ name: training_cpp_2021
 channels:
   - conda-forge
 dependencies:
-  - python>=3.8
-  - jupyterlab
-  - xeus-cling 
-  
\ No newline at end of file
+  - notebook
+  - xeus-cling=0.13.0
+  - gcc=9.4.0
\ No newline at end of file