Fix typo for grep (#2075)

Author: ahangarha

pry.md

@@ -95,7 +95,7 @@ Also consider [pry-rails](https://rubygems.org/gems/pry-rails).
 
     > ls -i      # Instance vars
 
-    > ls -G xx   # Grey by regex
+    > ls -G xx   # Grep by regex
 
 ## Shell integration