⏪ Revert "💚 Remove Appveyor cache for fixing build."

This reverts commit 4285fa4

Author: kayo5994

UI_dev/qmui_web/appveyor.yml

@@ -33,4 +33,8 @@ test_script:
   - gulp merge
 
 # Don't actually build.
-build: off
+build: off
+
+cache:
+  - C:\Users\appveyor\AppData\Roaming\npm-cache -> package.json # npm cache
+  - node_modules -> package.json                                # local npm modules