Use kotlin rather that JDK9

mirai-core/src/jvmMain/kotlin/net/mamoe/mirai/utils/PlatformUtilsJvm.kt

@@ -22,14 +22,15 @@ actual fun crc32(key: ByteArray): Int = CRC32().let { it.update(key); it.value.t
 actual fun md5(byteArray: ByteArray): ByteArray = MessageDigest.getInstance("MD5").digest(byteArray)
 
 fun InputStream.md5(): ByteArray = this.use {
-
     val digest = MessageDigest.getInstance("md5")
     digest.reset()
-    this.transferTo(object : OutputStream() {
+    this.use {
+        it.copyTo(object : OutputStream() {
             override fun write(b: Int) {
                 digest.update(b.toByte())
             }
         })
+    }
     return digest.digest()
 }