zplugin: Fix the bug #135 – inability to use periods (,) within //-subst
zplugin: Fix the bug #135 – inability to use periods (,) within //-subst

The bug occurs on zsh <= 5.3.1. The bug is that use of the period (,) is
impossible inside ${parameter//$arr[$(( ... ))]}.

psprint/zplugin,psprint/zplugin,psprint/zplugin