Get the momentjs lang by default

When you set the global language on momentjs, the datepicker set the language to english by default.
Is better to set this by the momentjs object.

I also fixed a minor error in line 47: requried -> required

src/js/bootstrap-datetimepicker.js

@@ -44,7 +44,7 @@
 (function ($, moment) {
     if (typeof moment === 'undefined') {
         alert("momentjs is requried");
-        throw new Error('momentjs is requried');
+        throw new Error('momentjs is required');
     };
 
     var dpgId = 0,
@@ -62,7 +62,7 @@
             startDate: new pMoment({ y: 1970 }),
             endDate: new pMoment().add(50, "y"),
             collapse: true,
-            language: "en",
+            language: pMoment.lang(),
             defaultDate: "",
             disabledDates: [],
             enabledDates: false,