Bootstrap Datepicker – Months and Years Only

How about this :

$("#datepicker").datepicker( {
    format: "mm-yyyy",
    viewMode: "months", 
    minViewMode: "months"
});

Reference : Datepicker for Bootstrap

For version 1.2.0 and newer, viewMode has changed to startView, so use:

$("#datepicker").datepicker( {
    format: "mm-yyyy",
    startView: "months", 
    minViewMode: "months"
});

Also see the documentation.