Select Java 8 for Travis CI

.travis.yml

@@ -1 +1,3 @@
 language: java
+jdk:
+  - openjdk8

README.md

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-# Parser and Interpreter for While Programs [![Build Status](https://travis-ci.org/malteschmitz/WhileInterpreter.svg?branch=master)](https://travis-ci.org/malteschmitz/WhileInterpreter)
+# Parser and Interpreter for While Programs [![Build Status](https://travis-ci.com/malteschmitz/WhileInterpreter.svg?branch=master)](https://travis-ci.com/malteschmitz/WhileInterpreter)
 
 Exemplary Java implementation of a _recursive decent parser_, an _abstract syntax tree (AST) data structure_ and a _structural recursive interpreter_ over this data structure.