upgrade back to kotlin 1.1.2-5 and removed older than 1.8 jdks

older than 1.8 jdks are not supported anymore:
https://blog.jetbrains.com/kotlin/2017/04/kotlin-1-1-2-is-out/#more-4945

Author: oshai

.travis.yml

@@ -2,7 +2,5 @@
 language: java
 jdk:
  - oraclejdk8
- - oraclejdk7
- - openjdk6
 
 script: gradle check

build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.1.1'
+    ext.kotlin_version = '1.1.2-5'
 
     repositories {
         mavenCentral()