Use autofunction to document approx.

kalekundert · kalekundert · commit b41852c93b2f · 2017-06-15T14:52:39.000-07:00
It used to be a class, but it's a function now.
diff --git a/doc/en/builtin.rst b/doc/en/builtin.rst
@@ -38,7 +38,7 @@ Examples at :ref:`assertraises`.
 Comparing floating point numbers
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-.. autoclass:: approx
+.. autofunction:: approx
 
 Raising a specific test outcome
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