Replace column name using reserved keyword

This commit replaces the "index" property of Review to use a custom
column name ("idx") as index is a reserved keyword in some RDMS such
as Oracle and MySQL.

Fixes gh-752

spring-boot-samples/spring-boot-sample-data-jpa/src/main/java/sample/data/jpa/domain/Review.java

@@ -43,7 +43,7 @@ public class Review implements Serializable {
 	@ManyToOne(optional = false)
 	private Hotel hotel;
 
-	@Column(nullable = false)
+	@Column(nullable = false, name = "idx")
 	private int index;
 
 	@Column(nullable = false)