Restore previous build-release command, failed on macOS

package.json

@@ -17,7 +17,7 @@
     "icon-gen": "electron-icon-maker --input=images/icon_1024.png --output=./build",
     "generate": "yarn icon-gen && yarn grunt",
     "build": "build  --config.extraMetadata.environment=$SIGNAL_ENV",
-    "build-release": "set SIGNAL_ENV=production && npm run build -- --config.directories.output=release && unset SIGNAL_ENV",
+    "build-release": "SIGNAL_ENV=production && npm run build -- --config.directories.output=release",
     "sign-release": "node ts/updater/generateSignature.js",
     "build-module-protobuf": "pbjs --target static-module --wrap commonjs --out ts/protobuf/compiled.js protos/*.proto && pbts --out ts/protobuf/compiled.d.ts ts/protobuf/compiled.js",
     "clean-module-protobuf": "rm -f ts/protobuf/compiled.d.ts ts/protobuf/compiled.js",