Update install.sh

Author: bbartels

src/node/install.sh

@@ -13,6 +13,7 @@ export NVM_VERSION="${NVMVERSION:-"latest"}"
 export NVM_DIR="${NVMINSTALLPATH:-"/usr/local/share/nvm"}"
 export NVM_NODEJS_ORG_MIRROR="${NVM_NODEJS_ORG_MIRROR:-https://nodejs.org/dist}"
 NVM_NODEJS_ORG_MIRROR_ESCAPED="$(printf '%q' "${NVM_NODEJS_ORG_MIRROR}")"
+GITHUB_USERCONTENT_URL="${GITHUB_USERCONTENT_MIRROR:-https://raw.githubusercontent.com}"
 INSTALL_TOOLS_FOR_NODE_GYP="${NODEGYPDEPENDENCIES:-true}"
 export INSTALL_YARN_USING_APT="${INSTALLYARNUSINGAPT:-false}"  # only concerns Debian-based systems
 
@@ -308,9 +309,9 @@ umask 0002
 # Do not update profile - we'll do this manually
 export PROFILE=/dev/null
 export NVM_NODEJS_ORG_MIRROR="${NVM_NODEJS_ORG_MIRROR}"
-curl -so- "https://raw.githubusercontent.com/nvm-sh/nvm/v${NVM_VERSION}/install.sh" | bash ||  {
+curl -so- "${GITHUB_USERCONTENT_URL}/nvm-sh/nvm/v${NVM_VERSION}/install.sh" | bash ||  {
     PREV_NVM_VERSION=$(curl -s https://api.github.com/repos/nvm-sh/nvm/releases/latest | grep '"tag_name"' | sed -E 's/.*"([^"]+)".*/\1/')
-    curl -so- "https://raw.githubusercontent.com/nvm-sh/nvm/\${PREV_NVM_VERSION}/install.sh" | bash
+    curl -so- "${GITHUB_USERCONTENT_URL}/nvm-sh/nvm/\${PREV_NVM_VERSION}/install.sh" | bash
     NVM_VERSION="\${PREV_NVM_VERSION}"
 }
 [ -s "${NVM_DIR}/nvm.sh" ] && source "${NVM_DIR}/nvm.sh"