Fix navy compilation issue

EnginePair.cpp file introduced in fc2f988
was not added to CMakeLists.txt which led to linking failure.

Author: igchor

cachelib/navy/CMakeLists.txt

@@ -35,6 +35,7 @@ add_library (cachelib_navy
   common/SizeDistribution.cpp
   common/Types.cpp
   driver/Driver.cpp
+  engine/EnginePair.cpp
   Factory.cpp
   scheduler/ThreadPoolJobScheduler.cpp
   scheduler/ThreadPoolJobQueue.cpp