fix: allow angular 8 peer dependency

Closes #898

Author: mattlewis92

package.json

@@ -126,9 +126,9 @@
     "zone.js": "^0.8.26"
   },
   "peerDependencies": {
-    "@angular/animations": ">=6.0.0 <8.0.0",
-    "@angular/common": ">=6.0.0 <8.0.0",
-    "@angular/core": ">=6.0.0 <8.0.0"
+    "@angular/animations": ">=6.0.0 <9.0.0",
+    "@angular/common": ">=6.0.0 <9.0.0",
+    "@angular/core": ">=6.0.0 <9.0.0"
   },
   "dependencies": {
     "angular-draggable-droppable": "^4.0.2",