Fix small typo

Author: lroellin

book/10-git-internals/sections/objects.asc

@@ -149,7 +149,7 @@ $ git cat-file -p 99f1a6d12cb4b6f19c8655fca46c3ecf317074e0
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 Depending on what shell you use, you may encounter errors when using the `master^{tree}` syntax.
 
-In PowerShell or CMD on Windows, the `^` character is used for escaping, so you have to double it to avoid this: `git cat-file -p mater^^{tree}`.
+In PowerShell or CMD on Windows, the `^` character is used for escaping, so you have to double it to avoid this: `git cat-file -p master^^{tree}`.
 
 If you're using ZSH, the `^` character is used for globbing, so you have to enclose the whole expression in quotes: `git cat-file -p "master^{tree}"`
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