use pyinstaller v4.0

from my maintenance branch in case I have to apply any fixes to get it working.

Vagrantfile

@@ -190,7 +190,7 @@ def install_pyinstaller()
     . borg-env/bin/activate
     git clone https://github.com/thomaswaldmann/pyinstaller.git
     cd pyinstaller
-    git checkout v3.5-maint
+    git checkout v4.0-maint
     python setup.py install
   EOF
 end