Update qterminal.install

Update qterminal.install because the file qterminal_drop.desktop was
renamed to qterminal-drop.desktop.

debian/qterminal.install

@@ -1,5 +1,5 @@
 usr/bin/qterminal
 usr/share/applications/qterminal.desktop
-usr/share/applications/qterminal_drop.desktop
+usr/share/applications/qterminal-drop.desktop
 usr/share/icons/hicolor/64x64/apps/qterminal.png
 usr/share/metainfo/qterminal.appdata.xml