fix dangling keyfunc examples in documentation of heapq and sorted (GH-1432)

* fix dangling mention of key=str.lower in heapq doc

* Fix dangling mention of keyfunc example for sorted()
(cherry picked from commit 6bdb6f7675922e601e742758c7c240a751fd365b)

Co-authored-by: Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de>
diff --git a/Doc/library/heapq.rst b/Doc/library/heapq.rst
index 0b1a3c8..8b00f7b 100644
--- a/Doc/library/heapq.rst
+++ b/Doc/library/heapq.rst
@@ -112,17 +112,17 @@
 
    Return a list with the *n* largest elements from the dataset defined by
    *iterable*.  *key*, if provided, specifies a function of one argument that is
-   used to extract a comparison key from each element in the iterable:
-   ``key=str.lower`` Equivalent to:  ``sorted(iterable, key=key,
-   reverse=True)[:n]``
+   used to extract a comparison key from each element in *iterable* (for example,
+   ``key=str.lower``).  Equivalent to:  ``sorted(iterable, key=key,
+   reverse=True)[:n]``.
 
 
 .. function:: nsmallest(n, iterable, key=None)
 
    Return a list with the *n* smallest elements from the dataset defined by
    *iterable*.  *key*, if provided, specifies a function of one argument that is
-   used to extract a comparison key from each element in the iterable:
-   ``key=str.lower`` Equivalent to:  ``sorted(iterable, key=key)[:n]``
+   used to extract a comparison key from each element in *iterable* (for example,
+   ``key=str.lower``).  Equivalent to:  ``sorted(iterable, key=key)[:n]``.
 
 
 The latter two functions perform best for smaller values of *n*.  For larger