"fishy" theme: Fix "~" use in prompt

Actually replace the value of the environment variable $HOME with
"~" instead of appending the tilde in front of the prompt.

themes/fishy.zsh-theme

@@ -5,7 +5,7 @@ _fishy_collapsed_wd() {
    BEGIN {
       binmode STDIN,  ":encoding(UTF-8)";
       binmode STDOUT, ":encoding(UTF-8)";
-   }; s|^$HOME|~|g; s|/([^/.])[^/]*(?=/)|/$1|g; s|/\.([^/])[^/]*(?=/)|/.$1|g;
+   }; s|^$ENV{HOME}|~|g; s|/([^/.])[^/]*(?=/)|/$1|g; s|/\.([^/])[^/]*(?=/)|/.$1|g
 ')
 }