Support 'snapshot' keyword

Updates language service package version which now includes snapshot:

- actions/languageservices#201

Author: lawrencegripper

package-lock.json

@@ -561,8 +561,8 @@
     "webpack-cli": "^4.10.0"
   },
   "dependencies": {
-    "@actions/languageserver": "^0.3.17",
-    "@actions/workflow-parser": "^0.3.17",
+    "@actions/languageserver": "^0.3.18",
+    "@actions/workflow-parser": "^0.3.18",
     "@octokit/rest": "^21.1.1",
     "@vscode/vsce": "^2.19.0",
     "buffer": "^6.0.3",
@@ -587,4 +587,4 @@
       "elliptic": "6.6.1"
     }
   }
-}
+}