Fix unit test failure at Java7

Author: sakama

build.gradle

@@ -23,7 +23,7 @@ dependencies {
     compile  "org.embulk:embulk-core:0.8.6"
     provided "org.embulk:embulk-core:0.8.6"
     // compile "YOUR_JAR_DEPENDENCY_GROUP:YOUR_JAR_DEPENDENCY_MODULE:YOUR_JAR_DEPENDENCY_VERSION"
-    compile "org.apache.commons:commons-vfs2:2.+"
+    compile "org.apache.commons:commons-vfs2:2.1.1660580.2"
     compile "com.jcraft:jsch:0.1.53"
     testCompile "junit:junit:4.+"
     testCompile "org.embulk:embulk-core:0.8.6:tests"