deps(yaml-cpp): specify that yaml-cpp is a dependency of OCIO

I'm not sure if this actually affects anything, since OCIO is a required dependency of OIIO; but if OCIO doesn't need to be built, then neither does yaml-cpp.

Signed-off-by: Zach Lewis <[email protected]>

src/cmake/externalpackages.cmake

@@ -133,7 +133,9 @@ checked_find_package (Freetype
                       DEFINITIONS USE_FREETYPE=1 )
 
 checked_find_package (yaml-cpp
-                      VERSION_MIN 0.6.0 )  # Used by OpenColorIO
+                      VERSION_MIN 0.6.0 
+                      ISDEPOF OpenColorIO
+                      )  # Used by OpenColorIO
 
 checked_find_package (OpenColorIO REQUIRED
                       VERSION_MIN 2.2