Update to the 0.0.12 release of the language server

This fixes a bug when parameter hints in addition to adding
documentation to ADD and COPY's --chown flag that was introduced in
Docker CE 17.09.

Signed-off-by: Remy Suen <remy.suen@gmail.com>

package.json

@@ -606,7 +606,7 @@
     "azure-arm-containerregistry": "^1.0.0-preview",
     "azure-arm-resource": "^2.0.0-preview",
     "azure-arm-website": "^1.0.0-preview",
-    "dockerfile-language-server-nodejs": "^0.0.11",
+    "dockerfile-language-server-nodejs": "^0.0.12",
     "dockerode": "^2.5.1",
     "moment": "^2.19.3",
     "opn": "^5.1.0",