URL for install_salesforce_cli outdated

Script Salesforce.gitlab-ci.yml references non-existing URL:
# Install Salesforce CLI mkdir sfdx CLIURL=https://developer.salesforce.com/media/salesforce-cli/sfdx-linux-amd64.tar.xz
Replace by 'https://developer.salesforce.com/media/salesforce-cli/sfdx/channels/stable/sfdx-linux-x64.tar.xz'