Remove support for Java 7 which is EOL

Author: Volker

.travis.yml

@@ -6,5 +6,4 @@ language: java
 jdk:
   - oraclejdk8
   - oraclejdk9
-  - openjdk7
 script: gradle check benchmark

README.md

@@ -11,7 +11,7 @@ JLessC is a [Less CSS compiler](http://lesscss.org) written completely in Java (
 
 Required Java Version
 ----
-JlessC requires Java SE 7 or higher. It is tested with Java SE 7 and 8 on [travis-ci.org](https://travis-ci.org/i-net-software/jlessc).
+JlessC requires Java SE 8 or higher. It is tested with Java SE 8 and 9 on [travis-ci.org](https://travis-ci.org/i-net-software/jlessc).
 
 
 Add Dependency