PipInstallTask: Connect to done() signal instead of finished()

Change-Id: I7a712791a440668c7efb8282d7f035a120c7d719
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/python/pipsupport.h

@@ -84,7 +84,7 @@ signals:
 
 private:
     void cancel();
-    void installFinished();
+    void handleDone();
     void handleOutput();
     void handleError();