fix typo

plugins/available/base.plugin.bash

@@ -33,7 +33,7 @@ pickfrom ()
     [ -z "$file" ] && reference $FUNCNAME && return
     length=$(cat $file | wc -l)
     n=$(expr $RANDOM \* $length \/ 32768 + 1)
-    head -n $n $f | tail -1
+    head -n $n $file | tail -1
 }
 
 pass ()