Remove irregular files, including symbolic links, from git ls-files.

[SamirTalwar]

Currently, if you run with project.git = true on a repository with symbolic links, we get an IOException.

No idea how to write a unit test for this (can't find any coverage for ScalafmtRunner). If it's OK to move this behavior into GitOps::lsTree, then it becomes easier to test. Please let me know!

Full stack trace when running with version 2.2.2:

Exception in thread "main" java.io.IOException: Is a directory
        at sun.nio.ch.FileDispatcherImpl.read0(Native Method)
        at sun.nio.ch.FileDispatcherImpl.read(FileDispatcherImpl.java:46)
        at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
        at sun.nio.ch.IOUtil.read(IOUtil.java:197)
        at sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:159)
        at sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:65)
        at sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:109)
        at sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:103)
        at java.nio.file.Files.read(Files.java:3105)
        at java.nio.file.Files.readAllBytes(Files.java:3158)
        at org.scalafmt.util.FileOps$.readFile(FileOps.scala:57)
        at org.scalafmt.util.FileOps$.readFile(FileOps.scala:48)
        at org.scalafmt.cli.InputMethod$FileContents.readInput(InputMethod.scala:44)
        at org.scalafmt.cli.ScalafmtDynamicRunner$.handleFile(ScalafmtDynamicRunner.scala:83)
        at org.scalafmt.cli.ScalafmtDynamicRunner$.$anonfun$run$4(ScalafmtDynamicRunner.scala:55)
        at org.scalafmt.cli.ScalafmtDynamicRunner$.$anonfun$run$4$adapted(ScalafmtDynamicRunner.scala:49)
        at scala.collection.immutable.List.foreach(List.scala:392)
        at org.scalafmt.cli.ScalafmtDynamicRunner$.$anonfun$run$3(ScalafmtDynamicRunner.scala:49)
        at scala.util.control.Breaks.breakable(Breaks.scala:42)
        at org.scalafmt.cli.ScalafmtDynamicRunner$.run(ScalafmtDynamicRunner.scala:49)
        at org.scalafmt.cli.Cli$.run(Cli.scala:96)
        at org.scalafmt.cli.Cli$.mainWithOptions(Cli.scala:69)
        at org.scalafmt.cli.Cli$.main(Cli.scala:58)
        at org.scalafmt.cli.Cli.main(Cli.scala)

[poslegm]

Thank you for this fix!

[SamirTalwar]

I forgot to explain why I changed f.toFile.delete() to deleteTree(f). The former wasn't actually deleting the directory (because it wasn't empty), it was just returning false, resulting in a lot of leftover temporary files. The latter actually deletes the files.

[SamirTalwar]

Cheers! Looking forward to v2.2.3!