fix qbs build

Change-Id: I99628c9a47fb4dfd13a18351499d42c1a488031d
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/projectexplorer.qbs

@@ -132,6 +132,7 @@ Project {
                 "settingsaccessor.cpp", "settingsaccessor.h",
                 "showineditortaskhandler.cpp", "showineditortaskhandler.h",
                 "showoutputtaskhandler.cpp", "showoutputtaskhandler.h",
+                "subscription.cpp", "subscription.h",
                 "target.cpp", "target.h",
                 "targetsettingspanel.cpp", "targetsettingspanel.h",
                 "targetsetuppage.cpp", "targetsetuppage.h",