Update conf.py

Author: mcbarton

docs/source/conf.py

@@ -15,7 +15,7 @@
                           find . -name "*";\
                           mamba create -n xeus-cpp-wasm-build emscripten_emscripten-wasm32==3.1.73 -c https://repo.prefix.dev/emscripten-forge-dev -y;\
                           mamba activate xeus-cpp-wasm-build;\
-                          mamba create -n environment-wasm-host nlohmann_json=3.12.0 xeus-lite xeus CppInterOp cpp-argparse pugixml doctest -c https://repo.prefix.dev/emscripten-forge-dev -y;\
+                          mamba create -n environment-wasm-host --platform emscripten-wasm32 nlohmann_json=3.12.0 xeus-lite xeus CppInterOp cpp-argparse pugixml doctest -c https://repo.prefix.dev/emscripten-forge-dev -y;\
                           mkdir build;\
                           cd build;\
                           export BUILD_PREFIX=$MAMBA_ROOT_PREFIX/envs/xeus-cpp-wasm-build;\