chore(grid-pinning): Fix typo in grid pinning spec

Author: dkamburov

projects/igniteui-angular/src/lib/grids/grid/grid.pinning.spec.ts

@@ -418,7 +418,7 @@ describe('IgxGrid - Column Pinning to End', () => {
     configureTestSuite();
 
     const COLUMN_HEADER_CLASS = '.igx-grid__th';
-    const FIRST_PINNED_CELL_CSS = '.igx-grid__td--pinned-first';
+    const FIRST_PINNED_CELL_CSS = 'igx-grid__td--pinned-first';
 
     beforeAll(async(() => {
         TestBed.configureTestingModule({