O código persistence.xml p/ quem não conseguiu achar.

<persistence xmlns="http://java.sun.com/xml/ns/persistence" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://java.sun.com/xml/ns/persistence 
    http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd" 
    version="2.0">

    <persistence-unit name="contas">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <class>br.com.alura.jpa.modelo.Conta</class>    

        <properties>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/alura_jpa "/>
            <property name="javax.persistence.jdbc.user" value="root" />
            <property name="javax.persistence.jdbc.password" value="Marinha22" />

            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>

            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
</persistence>