Fix grammar (it's -> its).
diff --git a/Doc/doc/doc.tex b/Doc/doc/doc.tex
index d16c414..ebebd91 100644
--- a/Doc/doc/doc.tex
+++ b/Doc/doc/doc.tex
@@ -617,7 +617,7 @@
Documentation for a ``simple'' macro. Simple macros are macros
which are used for code expansion, but which do not take
arguments so cannot be described as functions. This is not to
- be used for simple constant definitions. Examples of it's use
+ be used for simple constant definitions. Examples of its use
in the Python documentation include
\csimplemacro{PyObject_HEAD} and
\csimplemacro{Py_BEGIN_ALLOW_THREADS}.
@@ -812,7 +812,7 @@
The name of a ``simple'' macro. Simple macros are macros
which are used for code expansion, but which do not take
arguments so cannot be described as functions. This is not to
- be used for simple constant definitions. Examples of it's use
+ be used for simple constant definitions. Examples of its use
in the Python documentation include
\csimplemacro{PyObject_HEAD} and
\csimplemacro{Py_BEGIN_ALLOW_THREADS}.