Fix example AGSL code in the javadoc comments

 * uniform shader myShader;

 * vec4 main(vec2 canvas_coordinates) {

 *     // swap the red and blue color channels when sampling from myShader

 *     return myShader.sample(canvas_coordinates).bgra;

 *     return myShader.eval(canvas_coordinates).bgra;

 * }</pre>

 *

 * <p>After creating a {@link RuntimeShader} with that program the shader uniform can