Fix minor bug in JdbcIO example code

127  * <pre>{@code
128  * pipeline
129  *   .apply(...)
130  *   .apply(JdbcIO.<KV<Integer, String>>write()
131  *      .withDataSourceConfiguration(JdbcIO.DataSourceConfiguration.create(
132  *            "com.mysql.jdbc.Driver", "jdbc:mysql://hostname:3306/mydb")
133  *          .withUsername("username")
134  *          .withPassword("password"))
135  *      .withStatement("insert into Person values(?, ?)")
136  *      .withPreparedStatementSetter(new JdbcIO.PreparedStatementSetter<KV<Integer, String>>() {
137  *        public void setParameters(KV<Integer, String> element, PreparedStatement query)
138  *          throws SQLException {
139  *          query.setInt(1, kv.getKey());
140  *          query.setString(2, kv.getValue());
141  *        }
142  *      })
143  *    );
144  * }</pre>