fix java9 build (#119)

.travis.yml

@@ -15,29 +15,5 @@ matrix:
     jdk: oraclejdk8
   - scala: 2.13.0-M1
     jdk: oraclejdk8
-  - dist: trusty
-    group: edge
-    sudo: required
-    scala: 2.12.2
+  - scala: 2.12.2
     jdk: oraclejdk9
-    before_install:
-    - cd ~
-    - JDK9_URL=`curl http://jdk.java.net/9/ | grep "lin64JDK" | grep "tar.gz\"" | sed -e "s/\"/ /g" | awk '{print $5}'`
-    - wget -O jdk-9_linux-x64_bin.tar.gz $JDK9_URL
-    - tar -xzf jdk-9_linux-x64_bin.tar.gz
-    - cd -
-    script:
-    # https://github.com/sbt/sbt/pull/2951
-    - git clone https://github.com/retronym/java9-rt-export
-    - cd java9-rt-export/
-    - git checkout 1019a2873d057dd7214f4135e84283695728395d
-    - jdk_switcher use oraclejdk8
-    - sbt package
-#    - jdk_switcher use oraclejdk9
-    - export JAVA_HOME=~/jdk-9
-    - PATH=$JAVA_HOME/bin:$PATH
-    - mkdir -p $HOME/.sbt/0.13/java9-rt-ext; java -jar target/java9-rt-export-*.jar $HOME/.sbt/0.13/java9-rt-ext/rt.jar
-    - jar tf $HOME/.sbt/0.13/java9-rt-ext/rt.jar | grep java/lang/Object
-    - cd ..
-    - wget https://raw.githubusercontent.com/paulp/sbt-extras/9ade5fa54914ca8aded44105bf4b9a60966f3ccd/sbt && chmod +x ./sbt
-    - ./sbt -Dscala.ext.dirs=$HOME/.sbt/0.13/java9-rt-ext ++$TRAVIS_SCALA_VERSION test

build.sbt

@@ -60,13 +60,11 @@ javacOptions in compile ++= {
     case Some((2, v)) if v <= 11 =>
       Seq("-target", "6", "-source", "6")
     case _ =>
-      try {
-        scala.util.Properties.isJavaAtLeast("1.8")
+      if (scala.util.Properties.isJavaAtLeast("9")) {
+        // if Java9
+        Nil
+      } else {
         Seq("-target", "8")
-      } catch {
-        case _: NumberFormatException =>
-          // if Java9
-          Nil
       }
   }
 }

project/build.properties

@@ -1 +1 @@
-sbt.version=0.13.15
+sbt.version=0.13.17-RC1