Change scope of 'java.home' to machine-overridable

Signed-off-by: Sheng Chen <sheche@microsoft.com>

Author: jdneo

package.json

@@ -63,11 +63,13 @@
         "path": "./snippets/java.json"
       }
     ],
-    "grammars": [{
-			"language": "java",
-			"scopeName": "source.java",
-			"path": "./syntaxes/java.tmLanguage.json"
-		}],
+    "grammars": [
+      {
+        "language": "java",
+        "scopeName": "source.java",
+        "path": "./syntaxes/java.tmLanguage.json"
+      }
+    ],
     "jsonValidation": [
       {
         "fileMatch": "package.json",
@@ -85,7 +87,7 @@
           ],
           "default": null,
           "description": "Specifies the folder path to the JDK (11 or more recent) used to launch the Java Language Server.\nOn Windows, backslashes must be escaped, i.e.\n\"java.home\":\"C:\\\\Program Files\\\\Java\\\\jdk11.0_8\"",
-          "scope": "window"
+          "scope": "machine-overridable"
         },
         "java.jdt.ls.vmargs": {
           "type": [