Fix version returning null when running on Java 9

A bug in JDK-9 [JDK-8190987](https://bugs.openjdk.java.net/browse/JDK-8190987) caused `Package.getImplementationVersion()` to return null. This commits adds code to read the Manifest file from the JAR to get the Implementation Version when it's not possible to retreive the version through the normal way.

ktlint/src/main/kotlin/com/github/shyiko/ktlint/Main.kt

@@ -34,6 +34,7 @@ import java.io.FileNotFoundException
 import java.io.PrintStream
 import java.io.PrintWriter
 import java.math.BigInteger
+import java.net.URL
 import java.net.URLDecoder
 import java.nio.file.Path
 import java.nio.file.Paths
@@ -52,6 +53,7 @@ import java.util.concurrent.Future
 import java.util.concurrent.TimeUnit
 import java.util.concurrent.atomic.AtomicBoolean
 import java.util.concurrent.atomic.AtomicInteger
+import java.util.jar.Manifest
 import kotlin.system.exitProcess
 
 object Main {
@@ -220,7 +222,7 @@ ${ByteArrayOutputStream().let { this.printUsage(it); it }.toString().trimEnd().s
     fun main(args: Array<String>) {
         parseCmdLine(args)
         if (version) {
-            println(javaClass.`package`.implementationVersion)
+            println(version())
             exitProcess(0)
         }
         if (installGitPreCommitHook) {
@@ -430,6 +432,21 @@ ${ByteArrayOutputStream().let { this.printUsage(it); it }.toString().trimEnd().s
         }
     }
 
+    private fun version() = javaClass.`package`.implementationVersion ?: guessVersion()
+
+    private fun guessVersion(): String? {
+        //HACK: Workaround for https://bugs.openjdk.java.net/browse/JDK-8190987
+        val classFile = javaClass.simpleName + ".class"
+        val classPath = javaClass.getResource(classFile).toString()
+        if (!classPath.startsWith("jar")) return null
+
+        val manifestPath = classPath.substring(0, classPath.lastIndexOf("!") + 1) + "/META-INF/MANIFEST.MF"
+        val manifest = Manifest(URL(manifestPath).openStream())
+        val attributes = manifest.mainAttributes
+
+        return attributes.getValue("Implementation-Version")
+    }
+
     private fun fileSequence() =
         when {
             patterns.isEmpty() ->