use latest pip version

.devcontainer/Dockerfile

@@ -25,6 +25,7 @@ RUN groupadd --gid $USER_GID $USERNAME \
 ENV PATH="/home/${USERNAME}/.local/bin:${PATH}"
 
 # Install nicegui
+RUN pip install -U pip
 RUN pip install -U pip && pip install poetry==$POETRY_VERSION
 COPY nicegui pyproject.toml poetry.lock README.md ./
 RUN poetry install --all-extras