Fix a formatting error in the ast documentation.
diff --git a/Doc/library/ast.rst b/Doc/library/ast.rst
index 70840da..3c2f8d2 100644
--- a/Doc/library/ast.rst
+++ b/Doc/library/ast.rst
@@ -135,7 +135,7 @@
from untrusted sources without the need to parse the values oneself.
-.. function:: get_docstring(node, clean=True):
+.. function:: get_docstring(node, clean=True)
Return the docstring of the given *node* (which must be a
:class:`FunctionDef`, :class:`ClassDef` or :class:`Module` node), or ``None``