What does exit code 13 mean in CircleCI?

Question

I am trying to create and publish python package in Gemfury using CircleCI. But at the end the system shows message:
"Exited with code exit status 13"
"CircleCI received exit code 13"
So what does it mean? Also attach my sh file

    #!/bin/bash
    #Building packages and uploading them to a Gemfury repository

    GEMFURY_URL=$GEMFURY_PUSH_URL

    set -e

    DIRS="$@"
    BASE_DIR=$(pwd)
    SETUP="setup.py"

    warn() {
        echo "$@" 1>&2
    }

    die() {
        warn "$@"
        exit 1
    }

    build() {
        DIR="${1/%\//}"
        echo "Checking directory $DIR"
        cd "$BASE_DIR/$DIR"
        [ ! -e $SETUP ] && warn "No $SETUP file, skipping" && return
    PACKAGE_NAME=$(python $SETUP --fullname)
    echo "Package $PACKAGE_NAME"
    python "$SETUP" sdist bdist_wheel || die "Building package $PACKAGE_NAME failed"
    for X in $(ls dist)
    do
        curl -F package=@"dist/$X" "$GEMFURY_URL" || die "Uploading package $PACKAGE_NAME failed on file dist/$X"
    done
}

if [ -n "$DIRS" ]; then
    for dir in $DIRS; do
        build $dir
    done
else
    ls -d */ | while read dir; do
        build $dir
    done
fi

and screenshot: