Fix path to global ssh known hosts file

The path to the global known hosts file is /etc/ssh/ssh_known_hosts, not
/etc/ssh_hosts.

modules/completion/init.zsh

@@ -107,7 +107,7 @@ zstyle ':completion::*:(-command-|export):*' fake-parameters ${${${_comps[(I)-va
 zstyle -a ':prezto:module:completion:*:hosts' etc-host-ignores '_etc_host_ignores'
 
 zstyle -e ':completion:*:hosts' hosts 'reply=(
-  ${=${=${=${${(f)"$(cat {/etc/ssh_,~/.ssh/known_}hosts(|2)(N) 2> /dev/null)"}%%[#| ]*}//\]:[0-9]*/ }//,/ }//\[/ }
+  ${=${=${=${${(f)"$(cat {/etc/ssh/ssh_known_hosts,~/.ssh/known_hosts}(|2)(N) 2> /dev/null)"}%%[#| ]*}//\]:[0-9]*/ }//,/ }//\[/ }
   ${=${(f)"$(cat /etc/hosts(|)(N) <<(ypcat hosts 2> /dev/null))"}%%(\#${_etc_host_ignores:+|${(j:|:)~_etc_host_ignores}})*}
   ${=${${${${(@M)${(f)"$(cat ~/.ssh/config 2> /dev/null)"}:#Host *}#Host }:#*\**}:#*\?*}}
 )'