Update the pip inside the venv

update.sh

@@ -39,6 +39,8 @@ then
     $POEZIO_VENV_COMMAND --upgrade "$POEZIO_VENV"
 
     . "$POEZIO_VENV/bin/activate"
+    echo 'Updating the in-venv pip'
+    pip install --upgrade pip
     python3 -c 'import sys;(print("Python 3.4 or newer is required") and exit(1)) if sys.version_info < (3, 4) else exit(0)' || exit 1
     echo 'Updating the poezio dependencies'
     pip install -r requirements.txt --upgrade