fix(editors): use indexOf in multiple select editor to load value

indexOf must be used because defaultValue is an array. the current state
is broken and values are not loaded when the multiple select list is
opened

aurelia-slickgrid/src/aurelia-slickgrid/editors/multipleSelectEditor.ts

@@ -130,7 +130,7 @@ export class MultipleSelectEditor implements Editor {
     this.defaultValue = item[this.columnDef.field].map((i: any) => i.toString());
 
     this.$editorElm.find('option').each((i: number, $e: any) => {
-      if (this.defaultValue === $e.value) {
+      if (this.defaultValue.indexOf($e.value) !== -1) {
         $e.selected = true;
       } else {
         $e.selected = false;

aurelia-slickgrid/src/examples/slickgrid/example3.ts

@@ -159,7 +159,7 @@ export class Example3 {
       type: FieldType.string,
       editor: Editors.multipleSelect,
       params: {
-        collection: Array.from(Array(10).keys()).map(k => ({ value: `Task ${k}`, label: `Task ${k}` })),
+        collection: Array.from(Array(12).keys()).map(k => ({ value: `Task ${k}`, label: `Task ${k}` })),
         collectionSortBy: {
           property: 'label',
           sortDesc: true
@@ -213,7 +213,7 @@ export class Example3 {
         start: new Date(randomYear, randomMonth, randomDay),
         finish: new Date(randomYear, (randomMonth + 1), randomDay),
         effortDriven: (i % 5 === 0),
-        prerequisites: (i % 5 === 0) && i > 0 ? [`Task ${i}`, `Task ${i - 1}`] : []
+        prerequisites: (i % 2 === 0) && i !== 0 && i < 12 ? [`Task ${i}`, `Task ${i - 1}`] : []
       };
     }
     this.dataset = mockedDataset;