CPack: Fix PackageMaker .dmg HFS+ creation on macOS APFS hosts

When running `hdiutil create`, specify the HFS+ filesystem explicitly.
Otherwise `hdiutil` may choose a filesystem based on the host.  We do
not want to create APFS images for `.dmg` packages because they may not
mount on macOS versions prior to 10.12.

This was missed in commit 39b50975d9 (CPack: Fix .dmg HFS+ creation on
macOS APFS hosts, 2017-10-02).

Reported-by: Alan Garny

Source/CPack/cmCPackPackageMakerGenerator.cxx

@@ -288,8 +288,8 @@ int cmCPackPackageMakerGenerator::PackageFiles()
   tmpFile += "/hdiutilOutput.log";
   std::ostringstream dmgCmd;
   dmgCmd << "\"" << this->GetOption("CPACK_INSTALLER_PROGRAM_DISK_IMAGE")
-         << "\" create -ov -format UDZO -srcfolder \"" << packageDirFileName
-         << "\" \"" << packageFileNames[0] << "\"";
+         << "\" create -ov -fs HFS+ -format UDZO -srcfolder \""
+         << packageDirFileName << "\" \"" << packageFileNames[0] << "\"";
   std::string output;
   int retVal = 1;
   int numTries = 10;