DATAJDBC-264 - Fix insert statement for empty parameter list.

When an entity consists only of it's id column, the value list contained a single `:`.
This commit fixes this.

Original pull request: #88.

src/main/java/org/springframework/data/jdbc/core/SqlGenerator.java

@@ -260,7 +260,9 @@ class SqlGenerator {
 		columnNamesForInsert.addAll(additionalColumns);
 
 		String tableColumns = String.join(", ", columnNamesForInsert);
-		String parameterNames = columnNamesForInsert.stream().collect(Collectors.joining(", :", ":", ""));
+		String parameterNames = columnNamesForInsert.stream()//
+				.map(n -> String.format(":%s", n))//
+				.collect(Collectors.joining(", "));
 
 		return String.format(insertTemplate, entity.getTableName(), tableColumns, parameterNames);
 	}