Use toLowerCase() and toUpperCase() with Locale.ENGLISH

This commit updates all `toLowerCase()` and `toUpperCase` invocations to
use the variant that takes a `Locale` to avoid locale-specific side
effect.

Closes gh-12213

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/archive/ArchiveCommand.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@ import java.net.URL;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.jar.Manifest;
 
 import groovy.lang.Grab;
@@ -129,9 +130,10 @@ abstract class ArchiveCommand extends OptionParsingCommand {
 					+ this.type + " and at least one source file must be specified");
 
 			File output = new File((String) nonOptionArguments.remove(0));
-			Assert.isTrue(output.getName().toLowerCase().endsWith("." + this.type),
-					"The output '" + output + "' is not a " + this.type.toUpperCase()
-							+ " file.");
+			Assert.isTrue(
+					output.getName().toLowerCase(Locale.ENGLISH).endsWith("." + this.type),
+					"The output '" + output + "' is not a " + this.type.toUpperCase(
+							Locale.ENGLISH) + " file.");
 			deleteIfExists(output);
 
 			GroovyCompiler compiler = createCompiler(options);