removed obsolete electron version downgrade

.github/workflows/windows.yml

@@ -16,7 +16,6 @@ jobs:
     - name: Build
       shell: powershell
       run: |
-        yarn add -D electron@6.0.7
         yarn
         node scripts/build-native.js
         yarn run build

appveyor.yml

@@ -10,7 +10,6 @@ version: "{build}"
 
 install:
   - ps: Install-Product node $env:nodejs_version $env:platform
-  - yarn add -D electron@6.0.7
   - yarn
   - node scripts/build-native.js