ImageService(save): explicitly specify locale when calling String.toUpperCase().

Reported by PMD:
"When doing String.toLowerCase()/toUpperCase() conversions, use Locales to avoids
problems with languages that have unusual conventions, i.e. Turkish."

No functional changes.

Author: php-coder

src/main/java/ru/mystamps/web/service/ImageService.java

@@ -18,6 +18,7 @@
 package ru.mystamps.web.service;
 
 import java.io.IOException;
+import java.util.Locale;
 
 import javax.inject.Inject;
 
@@ -57,7 +58,7 @@ String save(final MultipartFile file) {
 		);
 
 		final Image image = new Image();
-		image.setType(Image.Type.valueOf(extension.toUpperCase()));
+		image.setType(Image.Type.valueOf(extension.toUpperCase(Locale.US)));
 
 		try {
 			image.setData(file.getBytes());