Windows 8.1 brought a few changes to the handy Windows-X shortcut menu, including a new Shut Down option and the addition of PowerShell shortcuts. There are plenty of good reasons to learn PowersShell, but if that's not for you, you can swap PowerShell for the Command Prompt.
Right-click on the taskbar and select Properties. Go to the Navigation tab and uncheck the box labelled "Replace Command Prompt with Windows PowerShell in the menu when I right-click the lower-left corner or press Windows-X." When you next use the Windows-X menu, you should see your familiar Command Prompt option return.