Default coveralls#timestampFormat to EpochMillis

[fdaugan]

When built from Travis, users can experience Unable to parse timestamp "13245678913": Unparseable date: "13245678913"
As recommanded is trautonen/coveralls-maven-plugin#91, update configuration to :

<plugin>
	<groupId>org.eluder.coveralls</groupId>
	<artifactId>coveralls-maven-plugin</artifactId>
	<configuration>
		<timestampFormat>EpochMillis</timestampFormat>
	</configuration>
</plugin>