Move pipenv creation from bootstrap to setup script

script/bootstrap

@@ -21,7 +21,6 @@ if [ -n "${CIBUILD}" ]; then
 fi
 
 # Install Python dependencies
-pipenv --python 3.6
 ${PIP_CMD} install --upgrade pip
 pipenv install ${PIPENV_INSTALL_FLAGS}
 

script/setup

@@ -11,6 +11,7 @@ cd "$(dirname "${0}")/.."
 
 # Install virtualenv
 pip install pipenv
+pipenv --python 3.6
 
 if ! type sass > /dev/null; then
   if type gem > /dev/null; then