Fix css classes indicating changed dates in timeline

app/assets/javascripts/angular/directives/timelines/timeline-column-data-directive.js

@@ -108,7 +108,7 @@ angular.module('openproject.timelines.directives')
         var oldDate = planningElement.historical_element[attr];
 
         if (oldDate && newDate) {
-          return (newDate < oldDate ? 'postponed' : 'preponed');
+          return (newDate < oldDate ? 'preponed' : 'postponed');
         }
         return "changed";
       }

karma/tests/directives/timelines/timeline-column-data-directive-test.js

@@ -85,7 +85,7 @@ describe('timelineColumnData Directive', function() {
 
       it('should assign a change kind class to the current date', function() {
         var container = element.find('.tl-column');
-        expect(container.hasClass('tl-preponed')).to.be.true;
+        expect(container.hasClass('tl-postponed')).to.be.true;
       });
 
       describe('the historical data container', function() {
@@ -99,7 +99,7 @@ describe('timelineColumnData Directive', function() {
         });
 
         it('should contain a link with a css class indicating the change', function() {
-          expect(historicalContainerElement.find('a').hasClass('tl-icon-preponed')).to.be.true;
+          expect(historicalContainerElement.find('a').hasClass('tl-icon-postponed')).to.be.true;
         });
       })
     });