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-samples/spring-boot-sample-data-gemfire/src/main/java/sample/data/gemfire/service/GemstoneServiceImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 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.
@@ -19,6 +19,7 @@ package sample.data.gemfire.service;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 
 import javax.annotation.PostConstruct;
 
@@ -126,7 +127,7 @@ public class GemstoneServiceImpl implements GemstoneService {
 	}
 
 	Gemstone validate(Gemstone gemstone) {
-		if (!APPROVED_GEMS.contains(gemstone.getName().toUpperCase())) {
+		if (!APPROVED_GEMS.contains(gemstone.getName().toUpperCase(Locale.ENGLISH))) {
 			// NOTE if the Gemstone is not valid, throw error...
 			// Should cause transaction to rollback in GemFire!
 			System.err.printf("Illegal Gemstone [%1$s]!%n", gemstone.getName());