Upgrade to libvips v8.9.0-rc4, drop support for Node.js 8

lib/operation.js

@@ -379,6 +379,8 @@ function linear (a, b) {
 /**
  * Recomb the image with the specified matrix.
  *
+ * @since 0.21.1
+ *
  * @example
  * sharp(input)
  *   .recomb([
@@ -416,6 +418,8 @@ function recomb (inputMatrix) {
 /**
  * Transforms the image using brightness, saturation and hue rotation.
  *
+ * @since 0.22.1
+ *
  * @example
  * sharp(input)
  *   .modulate({