fix typo in help

locale/en-US/options.txt

@@ -184,7 +184,7 @@ ____
 |\'editor'|
 ||'editor'|| string (default: "gvim -f")
 ____
-Set the external text editor
+Set the external text editor.
 Sets the editor to run when [m]<C-i>[m] is pressed in INSERT and TEXTAREA
 modes. +
 Warning: Vimperator will not behave correctly if the editor forks its own process,