chore(release): publish [skip ci]

- @ohif/extension-vtk@1.3.9
 - @ohif/core@2.6.8
 - @ohif/ui@1.4.2
 - @ohif/viewer@3.8.17

platform/core/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@ohif/core",
-  "version": "2.6.7",
+  "version": "2.6.8",
   "description": "Generic business logic for web-based medical imaging applications",
   "author": "OHIF Core Team",
   "license": "MIT",