Minor fix to STDOPTS definition

this is a very small fix to the CMake configuration to make LHCb usable in a CMake super-project.

/cc @rmatev

CMakeLists.txt

@@ -59,7 +59,7 @@ lhcb_env(
 # GAUDI_QMTEST_CLASS overwrites the default python class used for LHCb tests
 # Default is QMTTest, we use here an LHCb extension : LHCbTest
 lhcb_env(
-    SET STDOPTS ${CMAKE_SOURCE_DIR}/GaudiConf/options
+    SET STDOPTS ${CMAKE_CURRENT_SOURCE_DIR}/GaudiConf/options
     SET GAUDI_QMTEST_MODULE GaudiConf.QMTest.LHCbTest
     SET GAUDI_QMTEST_CLASS LHCbTest
 )