use svg for scalable icon

[proletarius101]

According to https://specifications.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html, a svg icon should be installed in $prefix/share/icons/hicolor/scalable/apps The icon in https://github.com/ProtonVPN/linux-app/blob/5a8b3e17fbc1dec788f14078916a5a8ac7eb0e49/protonvpn_gui/assets/img/vpn-logo.svg#L1 doesn't match the 1:1 standard for icons