Fix spectre includes

The include path should not be added to the include line, that will make
it be not found if the parent directory for includes is not included.

generators/spectre/generator_ghostview.h

@@ -13,7 +13,7 @@
 #include <core/generator.h>
 #include <interfaces/configinterface.h>
 
-#include <libspectre/spectre.h>
+#include <spectre.h>
 
 class GSGenerator : public Okular::Generator, public Okular::ConfigInterface
 {

generators/spectre/rendererthread.h

@@ -16,7 +16,7 @@
 #include <QString>
 #include <QThread>
 
-#include <libspectre/spectre.h>
+#include <spectre.h>
 
 class QImage;
 class GSGenerator;