Oracle JDK7 removed from build JDK10 added

[Oliver-Loeffler]

Closes #292 .

Oracle JDK7 is no longer officially supported and also no longer downloadable from Oracle JDK site. Therefore the oracle-jdk7 build was removed from Travis file.

Instead added:

• Open JDK8
• Open JDK10
• Oracle JDK10

References:

• http://www.oracle.com/technetwork/java/javase/downloads/index.html
• http://www.oracle.com/technetwork/java/javase/eol-135779.html
• http://www.webupd8.org/2017/06/why-oracle-java-7-and-6-installers-no.html

[vkostyukov]

Thanks @Oliver-Loeffler!