fix small typo

ch10_undo.md

@@ -260,7 +260,7 @@ The same set of arguments work with `:earlier` counterpart: `:later`.
 
 # Learn Undo the Smart Way
 
-`u` and `Ctrl-R` are two indispensable Vim commands. Learn them first. I do not use UNDO in my workflow, however I think it's good to be aware that it exists. Next, learn how to use `:earlier` and `:later` using the time argumentsfirst. After that, take your time to understand the undo tree. The [vim-mundo](https://github.com/simnalamburt/vim-mundo) plugin helped me a lot. Type along the texts in this chapter and check the undo tree as you make each change. Once you grasp it, you will never see undo system the same way again.
+`u` and `Ctrl-R` are two indispensable Vim commands. Learn them first. I do not use UNDO in my workflow, however I think it's good to be aware that it exists. Next, learn how to use `:earlier` and `:later` using the time arguments first. After that, take your time to understand the undo tree. The [vim-mundo](https://github.com/simnalamburt/vim-mundo) plugin helped me a lot. Type along the texts in this chapter and check the undo tree as you make each change. Once you grasp it, you will never see undo system the same way again.
 
 Prior to this chapter, you learned how to find any text in a project space, with undo, you can now find any text in a time dimension. You are now able to search for any text by its location and time written. You have achieved Vim-omnipresence.