By-pass failing removeUnusedImports step at Java 9 builds

See diffplug/spotless#83 for details.

.travis.yml

@@ -1,6 +1,6 @@
 language: java
 
-sudo: required
+sudo: true
 
 # required for oraclejdk9
 dist: trusty
@@ -13,19 +13,20 @@ addons:
   apt:
     packages:
       - oracle-java8-installer
+      - oracle-java9-installer
 
 matrix:
   allow_failures:
     - jdk: oraclejdk9
 
-before_cache:
-  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
-  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
+#before_cache:
+#  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+#  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
 
-cache:
-  directories:
-    - $HOME/.gradle/caches/
-    - $HOME/.gradle/wrapper/
+#cache:
+#  directories:
+#    - $HOME/.gradle/caches/
+#    - $HOME/.gradle/wrapper/
 
 # Display Gradle version instead of letting Travis execute './gradlew assemble' by default
 install: ./gradlew -version

build.gradle

@@ -385,7 +385,10 @@ subprojects { subproj ->
 			licenseHeaderFile headerFile, '(package|import) '
 			importOrderFile rootProject.file('src/eclipse/junit-eclipse.importorder')
 			eclipseFormatFile rootProject.file('src/eclipse/junit-eclipse-formatter-settings.xml')
-			removeUnusedImports()
+
+			if (org.gradle.api.JavaVersion.current() == org.gradle.api.JavaVersion.VERSION_1_8) {
+				removeUnusedImports()
+			}
 
 			trimTrailingWhitespace()
 			endWithNewline()