Run release_notes script in build_app.sh

Author: tanx

assets/script/build_app.sh

@@ -6,7 +6,10 @@ GOROOT=$HOME/go
 PATH=$GOPATH/bin:$GOROOT/bin:$PATH
 
 if [ "$(uname)" == "Darwin" ]; then
+  # build electron app for macOS
   npm run electron-pack -- --mac
+  # generate release notes only once
+  sh assets/script/release_notes.sh
 else
   # build binaries for windows
   cd assets/bin/win32