$ webdriver-manager update –standalone
Updating selenium standalone
downloading https://selenium-release.storage.googleapis.com/2.45/selenium-server-standalone-2.45.0.jar…
Updating chromedriver
downloading https://chromedriver.storage.googleapis.com/2.15/chromedriver_linux64.zip…
Error: Got error Error: tunneling socket could not be established, cause=connect EINVAL from https://selenium-release.storage.googleapis.com/2.45/selenium-server-standalone-2.45.0.jar
Error: Got error Error: tunneling socket could not be established, cause=connect EINVAL from https://chromedriver.storage.googleapis.com/2.15/chromedriver_linux64.zip

Cause: You are using proxy with http_proxy and https_proxy not in the format http://IP:PORT
For example:

Not working:
http_proxy=http://172.16.1.5:80/
https_proxy=https://172.16.1.5:80/
http_proxy=172.16.1.5:80
https_proxy=172.16.1.5:80

Working:
http_proxy=http://172.16.1.5:80
https_proxy=http://172.16.1.5:80