Updated notification after update

The notification which draws the attention to  the
changelog after each update of the extension is no longer displayed by default. But it can still be enabled with `"material-icon-theme.showUpdateMessage": true` in the user settings.

References #225

package.json

@@ -79,7 +79,7 @@
         },
         "material-icon-theme.showUpdateMessage": {
           "type": "boolean",
-          "default": true,
+          "default": false,
           "description": "%configuration.showUpdateMessage%"
         },
         "material-icon-theme.activeIconPack": {

src/messages/update.ts

@@ -8,7 +8,7 @@ import { activateIconTheme } from '../commands/activate';
 /** Show the update message if the icon theme has been updated. */
 export const showUpdateMessage = () => {
     // if the user does not want to see the update message
-    if (helpers.getThemeConfig('showUpdateMessage').globalValue === false) return;
+    if (helpers.getThemeConfig('showUpdateMessage').globalValue !== true) return;
 
     const config = helpers.getConfig().inspect('workbench.iconTheme');