mingw-spec: Update msitools dependency
    
    The new msitools release includes the necessaries changes for fixing
    mingw-virt-viewer build (on fedora22).
    
    These fixes are:
    - an updated libvirt.wxi, removing storageencryption.rng file
    - a new included libeproxy.wxi, a new dep for gtk3 since its 3.15.3
      version.