fix travis wine build

.travis.yml

@@ -33,7 +33,7 @@ jobs:
         - sudo apt-key add Release.key
         - sudo apt-add-repository https://dl.winehq.org/wine-builds/ubuntu/
         - sudo apt-get update -qq
-        - sudo apt-get install -qq winehq-stable dirmngr gnupg2 p7zip-full
+        - sudo apt-get install -qq winehq-stable dirmngr gnupg2 p7zip-full mingw-w64
       before_script: ls -lah /tmp/electrum-build
       script: ./contrib/build-wine/build.sh
       after_success: true