Refine the fix for examples breakage (#207)

examples/boto/requirements.txt

diff --git a/examples/boto/requirements.txt b/examples/boto/requirements.txt
index b890060..12d0b6f 100644
--- a/examples/boto/requirements.txt
+++ b/examples/boto/requirements.txt
@@ -1,4 +1,4 @@
 boto3==1.4.7
 # Release 0.15 appears to have a broken wheel.
 # See https://github.com/bazelbuild/rules_python/issues/205.
-docutils<0.15
+docutils!=0.15.post1