cmake: fix install target

This change allows install from build directories that are not the source
directory.  PROGRAMS are part of the source directory while TARGETS/RUNTIME
are executibles generated by the build.  I've gotten this right in other
projects, just messed it up here.

tl;dr: s/PROGRAMS/TARGETS/

CMakeLists.txt

@@ -19,4 +19,4 @@ set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${RENDERER_FLAGS}" )
 add_executable( rpiplay rpiplay.cpp)
 target_link_libraries ( rpiplay renderers airplay )
 
-install(PROGRAMS rpiplay DESTINATION bin)
+install(TARGETS rpiplay RUNTIME DESTINATION bin)