Fix docstring bug
diff --git a/Lib/decimal.py b/Lib/decimal.py
index 6dc7398..2b9bc75 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -487,7 +487,7 @@
     28
     >>> with localcontext():
     ...     ctx = getcontext()
-    ...     ctx.prec() += 2
+    ...     ctx.prec += 2
     ...     print ctx.prec
     ...
     30