Fix image loading example in README

Author: adrhill

README.md

@@ -24,14 +24,14 @@ Let's use LRP to explain why an image of a castle gets classified as such using
 using ExplainableAI
 using Flux
 using Metalhead
-using FileIO
+using FileIO, HTTP
 
 # Load model
 model = VGG(16, pretrain=true).layers
 model = strip_softmax(flatten_chain(model))
 
 # Load input
-url = "https://raw.githubusercontent.com/adrhill/ExplainableAI.jl/gh-pages/assets/heatmaps/castle.jpg"
+url = HTTP.URI("https://raw.githubusercontent.com/adrhill/ExplainableAI.jl/gh-pages/assets/heatmaps/castle.jpg")
 img = load(url)
 input = preprocess_imagenet(img)
 input = reshape(input, 224, 224, 3, :)  # reshape to WHCN format