fixed wrong return type in performance timer

cmake @ fbc7a6c6

-Subproject commit 809ae57efe0fb1b44c069aacfabd3f5f988cafdb
+Subproject commit fbc7a6c6d438fd390368709eb7727f3a522bfe27

include/ACGL/Utils/PerformanceTimer.hh

@@ -65,7 +65,7 @@ private:
         return ( _time.tv_sec*1000000000 + _time.tv_nsec );
     }
 
-    inline uint64_t timespecToDouble( const timespec &_time ) const {
+    inline double timespecToDouble( const timespec &_time ) const {
         return ( _time.tv_sec + _time.tv_nsec/1000000000.0 );
     }