Disregard case when checking file extensions

Author: mkhl

.gitignore

@@ -4,6 +4,7 @@
 /package-lock.json
 
 # Ignore the images
+*.JPEG
 *.jpg
 *.png
 *.webp

index.js

@@ -151,5 +151,5 @@ function withFileExtension(...extensions) {
 
 // extname follows this annoying idea that the dot belongs to the extension
 function extname(filename) {
-	return path.extname(filename).slice(1);
+	return path.extname(filename).slice(1).toLowerCase();
 }

test/prepare

@@ -7,6 +7,8 @@ curl -C - -o "test/test_basic/src/example.gif" "https://upload.wikimedia.org/wik
 curl -C - -o "test/test_basic/src/example.svg" "https://upload.wikimedia.org/wikipedia/commons/0/02/SVG_logo.svg"
 curl -C - -o "test/test_basic/src/example.webp" "https://www.gstatic.com/webp/gallery3/2_webp_a.webp"
 
+cp test/test_basic/src/example.jpg test/test_basic/src/UPPERCASE.JPEG
+
 cp test/test_basic/src/example.jpg test/test_webp/src/example.jpg
 cp test/test_basic/src/example.png test/test_webp/src/example.png
 cp test/test_basic/src/example.webp test/test_webp/src/example.webp

test/run

@@ -54,6 +54,9 @@ begin "$root/test_basic"
 	assert_smaller_size src/example.jpg dist/example.jpg
 	assert_mime_type "image/jpeg" dist/example.jpg
 
+	assert_smaller_size src/UPPERCASE.JPEG dist/UPPERCASE.JPEG
+	assert_mime_type "image/jpeg" dist/UPPERCASE.JPEG
+
 	assert_smaller_size src/example.png dist/example.png
 	assert_mime_type "image/png" dist/example.png