Update prometheus-install.sh

Add `version.txt`

Author: tteck

install/prometheus-install.sh

@@ -29,6 +29,7 @@ cd prometheus-${RELEASE}.linux-amd64
 mv prometheus promtool /usr/local/bin/
 mv consoles/ console_libraries/ /etc/prometheus/
 mv prometheus.yml /etc/prometheus/prometheus.yml
+echo "${RELEASE}" >/opt/${APPLICATION}_version.txt
 msg_ok "Installed Prometheus"
 
 msg_info "Creating Service"