tmux: Fix version checking.
tmux: Fix version checking.

We need to remove letters from the version as tmux uses letter to indicate
patch releases. For example, at the time of writing, the current tmux version
is `3.0a`. However,

    tmux -V | cut -d" " -f2) < 2.1" | bc

fails with

    (standard_in) 1: syntax error

because

    tmux -V | cut -d" " -f2) < 2.1"

produces

    3.0a >= 2.6

and `3.0a` is not a valid number. Removing letters from the version fixes that.

s3rvac/dotfiles,s3rvac/dotfiles,s3rvac/dotfiles