Fix arrow keys when using true color config

[paulodiovani]

I notice the arrow keys doesn't work when setting tmux to use true color, required for some color schemes.

This PR fix that by allowing the :Tc suffix in the term regex.

More info at:

• https://github.com/rakr/vim-one#tmux-support
• http://homeonrails.com/2016/05/truecolor-in-gnome-terminal-tmux-and-neovim/

My (g)vim version:

local/gvim 8.1.2102-1
    Vi Improved, a highly configurable, improved version of the vi text editor (with advanced features, such as a GUI)
local/vim-runtime 8.1.2102-1
    Vi Improved, a highly configurable, improved version of the vi text editor (shared runtime)

[mattn]

Currently it checks with =~? (? mean ignroecase)

[mattn]

Thank you