Move function out of companion object

ultrasonic/src/main/kotlin/org/moire/ultrasonic/service/DownloadFile.kt

@@ -351,7 +351,6 @@ class DownloadFile(
         }
     }
 
-    companion object {
     private fun updateModificationDate(file: File) {
         if (file.exists()) {
             val ok = file.setLastModified(System.currentTimeMillis())
@@ -363,6 +362,7 @@ class DownloadFile(
                 try {
                     // Try alternate method to update last modified date to current time
                     // Found at https://code.google.com/p/android/issues/detail?id=18624
+                    // According to the bug, this was fixed in Android 8.0 (API 26)
                     val raf = RandomAccessFile(file, "rw")
                     val length = raf.length()
                     raf.setLength(length + 1)
@@ -375,4 +375,3 @@ class DownloadFile(
         }
     }
 }
-}