Update bootstrap-datetimepicker.js

if (this.viewSelect >= 3) {
    this._setDate(UTCDate(year, month, day, hours, minutes, seconds, 0));
}

there is a bug:the day value may be 31,UTCDate(2013, 6, 31...) renturn the next month 7, when i only chose month(startView=3, minView=3)  
Merge pull request #43 from xiatian/master

a bug in chose month, very few cases