dub tip for building tkd application

[Alain De Vos]

On unix systems the tcltk library files can have different 
namings and versions and dub build might not be able to link 
correctly.

After a failing build dependencies are found in ~/.dub/packages
In the file ~/.dub/packages/tcltk-8.6.5/tcltk/dub.json you can 
edit for the specific libraries as installed on your O.S.,
In my case :
"libs-posix": [
		"tcl87",
		"tk87"
	],