fix(core): dowgrade to previous SlickGrid version to fix issues

- last and recent SlickGrid version causes 2 issues that were caught by the Cypress E2E tests, downgrading to 2.4.11 fixes that

Author: Ghislain Beaulac

package.json

@@ -88,7 +88,7 @@
     "lodash.isequal": "^4.5.0",
     "moment-mini": "^2.22.1",
     "rxjs": "^6.3.3",
-    "slickgrid": "^2.4.11",
+    "slickgrid": "2.4.11",
     "text-encoding-utf-8": "^1.0.2",
     "tslib": "^1.9.3",
     "vinyl-paths": "^2.1.0"