Fixing blend state warning

src/animation/blend_state.cpp

diff --git a/src/animation/blend_state.cpp b/src/animation/blend_state.cpp
index b52e804..856514d 100644
--- a/src/animation/blend_state.cpp
+++ b/src/animation/blend_state.cpp
@@ -1,4 +1,5 @@
 #include "animation/blend_state.hpp"
+#include "animation/blend_animation.hpp"
 
 using namespace rive;