Bump version to 2.1.9

- Substitute occurrences of "2.1.8" with "2.1.9" using:
  git grep -I -l -e '2\.1\.8' | xargs \
  sed -b -i -e 's/2\.1\.8/2\.1\.9/g'

CUETools.Codecs.TTA/AssemblyInfo.cpp

@@ -29,7 +29,7 @@ using namespace System::Security::Permissions;
 // You can specify all the value or you can default the Revision and Build Numbers
 // by using the '*' as shown below:
 
-[assembly:AssemblyVersionAttribute("2.1.8.0")];
+[assembly:AssemblyVersionAttribute("2.1.9.0")];
 
 [assembly:ComVisible(false)];