Move majorLables to 1st week in the month, for 'week' scale

* next() always adds 1 week to current date
* show 1st week in the month as majorLabel

lib/timeline/TimeStep.js

@@ -222,23 +222,7 @@ TimeStep.prototype.next = function() {
       break;
     case 'weekday':      // intentional fall through
     case 'day':          this.current.add(this.step, 'day'); break;
-    case 'week':
-      if (this.current.weekday() !== 0){ // we had a month break not correlating with a week's start before
-        this.current.weekday(0); // switch back to week cycles
-        this.current.add(this.step, 'week');
-      } else if(this.options.showMajorLabels === false) {
-        this.current.add(this.step, 'week'); // the default case
-      } else { // first day of the week
-        var nextWeek = this.current.clone();
-        nextWeek.add(1, 'week');
-        if(nextWeek.isSame(this.current, 'month')){ // is the first day of the next week in the same month?
-          this.current.add(this.step, 'week'); // the default case
-        } else { // inject a step at each first day of the month
-          this.current.add(this.step, 'week');
-          this.current.date(1);
-        }
-      }
-      break;
+    case 'week':         this.current.add(this.step, 'week'); break;
     case 'month':        this.current.add(this.step, 'month'); break;
     case 'year':         this.current.add(this.step, 'year'); break;
     default: break;
@@ -548,7 +532,7 @@ TimeStep.prototype.isMajor = function() {
     case 'day':
       return (date.date() == 1);
     case 'week':
-      return (date.date() == 1);
+      return (Math.ceil(date.date() / 7) == 1); // is 1st week in the month?
     case 'month':
       return (date.month() == 0);
     case 'year':