Update CImg to 3.4.0 (#4377)

packages/c/cimg/xmake.lua

@@ -9,6 +9,7 @@ package("cimg")
     end})
     add_urls("https://github.com/greyclab/cimg.git")
 
+    add_versions("v3.4.0", "987bddc3a98ec684c2ffc7968881adb2626f5b09c90e6102947b3c4acd0de931")
     add_versions("v3.3.6", "7bb6621c38458152f3d1cae3f020e4ca6a314076cb7b4b5d6bbf324ad3d0ab88")
     add_versions("v3.2.6", "1fcca9a7a453aa278660c10d54c6db9b4c614b6a29250adeb231e95a0be209e7")