Update build settings

Author: takezoe

.travis.yml

@@ -2,5 +2,9 @@ sudo: false
 language: scala
 jdk:
 - oraclejdk8
+cache:
+  directories:
+  - "$HOME/.ivy2"
+  - "$HOME/.sbt"
 script:
-- ./build-gitbucket-plugin.sh
+- sbt test

build-gitbucket-plugin.sh

@@ -2,7 +2,7 @@ organization := "io.github.gitbucket"
 name := "gitbucket-gist-plugin"
 version := "4.11.0"
 scalaVersion := "2.12.4"
-gitbucketVersion := Option(System.getProperty("gitbucket.version")).getOrElse("4.19.0")
+gitbucketVersion := "4.19.0"
 
 scalacOptions := Seq("-deprecation", "-feature", "-language:postfixOps")
 javacOptions in compile ++= Seq("-target", "8", "-source", "8")