clarified versions -- more reproducible build;

--- a/src/Tools/VSCode/extension/package.json	Thu Feb 27 12:18:16 2020 +0100
+++ b/src/Tools/VSCode/extension/package.json	Thu Feb 27 12:27:49 2020 +0100
@@ -10,7 +10,7 @@
         "document preparation"
     ],
     "icon": "isabelle.png",
-    "version": "1.2.0",
+    "version": "1.2.1",
     "publisher": "makarius",
     "license": "MIT",
     "repository": {
@@ -291,6 +291,7 @@
         "vscode": "^1.1.36"
     },
     "dependencies": {
-        "vscode-languageclient": "~3.2.2"
+        "vscode-languageclient": "~3.2.2",
+        "vscode-languageserver-types": "~3.14.0"
     }
 }