Ghaction upload (#3)

Modifying gh action to upload xpi artifact

.github/workflows/build.yml

@@ -23,3 +23,7 @@ jobs:
         run: npm run lint:js
       - name: Build XPI
         run: npm run build
+      - uses: actions/upload-artifact@v2
+        with:
+          name: Extension-XPI
+          path: web-ext-artifacts/firefox_translations-*.zip