core: use Core::Id for IVersionControl::id()

Change-Id: I54e17c91c3e2a69d598ed485235dbf7ec62b4615
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/git/gitversioncontrol.h

@@ -48,7 +48,7 @@ public:
     explicit GitVersionControl(GitClient *plugin);
 
     QString displayName() const;
-    QString id() const;
+    Core::Id id() const;
 
     bool managesDirectory(const QString &directory, QString *topLevel) const;