Ensure that jar entry names use forward slashes, even on Windows

Previously, in the DevTools integration tests, portions of a File's
path were used to create the name of a jar entry. On Windows this
resulted in the entry containing \ characters. As a result the
directory structure was incorrect and the classes could not be loaded
from the jar.

This commit ensures that any \ characters are replaced with /
characters.

See gh-7782

spring-boot-integration-tests/spring-boot-devtools-tests/src/test/java/org/springframework/boot/devtools/tests/JarFileRemoteApplicationLauncher.java

 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -70,7 +70,7 @@ public class JarFileRemoteApplicationLauncher extends RemoteApplicationLauncher
 			}
 			output.putNextEntry(new ZipEntry(
 					file.getAbsolutePath().substring(root.getAbsolutePath().length() + 1)
-							+ (file.isDirectory() ? "/" : "")));
+							.replace("\\", "/") + (file.isDirectory() ? "/" : "")));
 			if (file.isFile()) {
 				StreamUtils.copy(new FileInputStream(file), output);
 			}