Merge pull request #100 from elchamopablo/patch-1

Update n_151_01.md

book/notes/n_151_01.md

@@ -7,6 +7,6 @@ of the core functionality of the UNIX `cat` command.  Part of the philosophy of
 commands that are each simple building blocks that can be composed using standard input and output
 redirection as well as pipes.
 
-These next two sections are a gentle celebration of the design principles that underly the UNIX operating
+These next two sections are a gentle celebration of the design principles that underlie the UNIX operating
 system.  Also, while we are talking about the linkage between C and UNIX, there is a UNIX-related
 Easter Egg earlier in this chapter.  See if you can find it.  Bonus points if you already noticed it. :)