dot/zshrc: Fix arguments to the hooks.

dot/zshrc: Fix arguments to the hooks.

The `precmd' hook doesn't take an argument -- what would it say anyway?
The `preexec' hook should have the command, only without newlines,
because otherwise the newline aborts the set-title control sequence,
and (a) the title doesn't get changed after all, and (b) lines after the
first get spammed to the terminal output.

Fortunately, `zsh' provides a version of the command without the
newlines, which looks purpose-built for this application.