style: declare globals properly

By default, `typeset` defines variables locally unless in the main scope.
This is specially bad when using `omz plugin load`, which happens inside
a function, so the declared variables don't continue being defined when
the function finishes and the main scope reappears.

plugins/colored-man-pages/colored-man-pages.plugin.zsh

@@ -22,7 +22,7 @@ less_termcap[ue]="${reset_color}"
 0="${${(M)0:#/*}:-$PWD/$0}"
 
 # Absolute path to this file's directory.
-typeset __colored_man_pages_dir="${0:A:h}"
+typeset -g __colored_man_pages_dir="${0:A:h}"
 
 function colored() {
   local -a environment