Fix windows binary build

Adds "experimental" tag to the windows binary build so that it
recognizes `routing.assumechanvalid` flag.

Author: Karl Ranna

assets/script/build_app.sh

@@ -10,7 +10,7 @@ if [ "$(uname)" == "Darwin" ]; then
 else
   # build binaries for windows
   cd assets/bin/win32
-  env GOOS="windows" GOARCH="386" go build -v github.com/lightningnetwork/lnd
+  env GOOS="windows" GOARCH="386" go build -v -tags="experimental" github.com/lightningnetwork/lnd
   env GOOS="windows" GOARCH="386" go build -v github.com/btcsuite/btcd
 
   # build the packages using electron-builder on docker