Fix transferfunction usage so it binds texture

include/openspace/rendering/transferfunction.h

@@ -43,7 +43,7 @@ public:
     void setPath(const std::string& filepath);
     ghoul::opengl::Texture& getTexture();
     void bind();
-    void updateTexture();
+    void update();
     glm::vec4 sample(size_t t);
     size_t width();
     void setCallback(TfChangedCallback callback);