Fix compiler warnings

[warn] LubyTransform.scala:57: implicit conversion method file2buffer should be enabled
[warn] by making the implicit value scala.language.implicitConversions visible.
[warn] This can be achieved by adding the import clause 'import scala.language.implicitConversions'
[warn] or by setting the compiler option -language:implicitConversions.
[warn] See the Scala docs for value scala.language.implicitConversions for a discussion
[warn] why the feature should be explicitly enabled.
[warn]     implicit def file2buffer (file: File): ByteBuffer = new FileInputStream(file).getChannel.map(READ_ONLY, 0, file.length)
[warn]                  ^
[warn] LubyTransform.scala:124: postfix operator contains should be enabled
[warn] by making the implicit value scala.language.postfixOps visible.
[warn] This can be achieved by adding the import clause 'import scala.language.postfixOps'
[warn] or by setting the compiler option -language:postfixOps.
[warn] See the Scala docs for value scala.language.postfixOps for a discussion
[warn] why the feature should be explicitly enabled.
[warn]         val remaining = block.chunks filterNot (intersection contains)
[warn]                                                              ^
[warn] LubyTransform.scala:211: implicit conversion method int2bigdecimal should be enabled
[warn] by making the implicit value scala.language.implicitConversions visible.
[warn]     implicit def int2bigdecimal (v: Int) = BigDecimal(v)
[warn]                  ^
[warn] three warnings found