Use DOWNLOAD_URL env var in install-nightly-toolchain

Author: MaxDesiatov

utils/webassembly/install-nightly-toolchain.sh

@@ -16,7 +16,7 @@ install_linux() {
 
   DOWNLOAD_DIR=$(echo $download | sed "s/-ubuntu18.04.tar.gz//g")
   DOWNLOAD_URL=${BASE_URL}/ubuntu1804/${DOWNLOAD_DIR}/${download}
-  /usr/bin/curl ${BASE_URL}/${DOWNLOAD_DIR}/${download} > ${WORKSPACE}/latest_toolchain.tar.gz
+  /usr/bin/curl $DOWNLOAD_URL > ${WORKSPACE}/latest_toolchain.tar.gz
 
   mkdir -p ${WORKSPACE}/latest_toolchain
   tar xzf ${WORKSPACE}/latest_toolchain.tar.gz -C ${WORKSPACE}/latest_toolchain