Drop support for java jdk1.6

Author: S L

.travis.yml

@@ -2,4 +2,3 @@ language: java
 jdk:
   - oraclejdk8
   - oraclejdk7
-  - openjdk6

pom.xml

@@ -76,7 +76,7 @@
     <junit.version>4.12</junit.version>
     <mockito.version>2.0.5-beta</mockito.version>
 
-    <java.target>1.6</java.target>
+    <java.target>1.7</java.target>
     <sourceEncoding>UTF-8</sourceEncoding>
     <outputEncoding>UTF-8</outputEncoding>
     <fest-assert.version>1.4</fest-assert.version>