Update windows-package-manager.rst Firefox pkg name was changed to lowercase
Update windows-package-manager.rst Firefox pkg name was changed to lowercase

The salt winrepo firefox.sls pkg name for 'Firefox' has changed to lowercase 'firefox' in salt-winrepo commit SHA: c821f53
saltstack/salt-winrepo@SHA: saltstack/salt-winrepo@c821f53
https://github.com/saltstack/salt-winrepo/commit/c821f539b00dcff865a3e4144406df0a6d8430df#diff-e4cafcf2dc2edcf281c42447df0fdfa5
saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt