update java version to 1.8

.travis.yml

@@ -1,6 +1,6 @@
 language: java
 sudo: false
 jdk:
-  - oraclejdk7
+  - oraclejdk8
 after_success:
   - mvn clean cobertura:cobertura coveralls:report

pom.xml

@@ -25,7 +25,7 @@
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <java.version>1.7</java.version>
+        <java.version>1.8</java.version>
         <junit.version>4.12</junit.version>
         <assertj.version>2.6.0</assertj.version>
         <mockito.version>2.7.1</mockito.version>