update window properties in desktop file

[danieltomasz]

please update window properties in shipped .desktop file for snap release
After checking with the xprop the proper value should be StartupWMClass=pocket-casts

With the current value, it doesn't group properly on some docks.

[danieltomasz]

For some Linux docks (like plank) it cause two instances of the app (one pinned launcher to dock and one running instance without icon).
In the .desktop file entry StartupWMclass has different value that the name the xprop shows when used on active window.

I dont know much about electron, they mention the same issue here electron-userland/electron-builder#2598

[metya]

I just rewrite StartupWMClass=Pocket Casts with pocket-casts, but nothing changes. On my taskbar icon of the app is still blank.
How can i fix it?