feat: add optional peer dependencies on date-fns and moment

Closes #1095

Author: mattlewis92

package.json

@@ -143,7 +143,17 @@
   "peerDependencies": {
     "@angular/animations": ">=6.0.0 <10.0.0",
     "@angular/common": ">=6.0.0 <10.0.0",
-    "@angular/core": ">=6.0.0 <10.0.0"
+    "@angular/core": ">=6.0.0 <10.0.0",
+    "date-fns": "^2.0.0",
+    "moment": "^2.0.0"
+  },
+  "peerDependenciesMeta": {
+    "date-fns": {
+      "optional": true
+    },
+    "moment": {
+      "optional": true
+    }
   },
   "dependencies": {
     "angular-draggable-droppable": "^4.3.8",