adopt review comment of #1186

MANIFEST.in

@@ -10,10 +10,13 @@ include setup.py
 
 include .coveragerc
 
+include plugin-test.sh
+include requirements-docs.txt
+include runtox.py
+
 recursive-include bench *.py
 recursive-include extra *.py
 
-
 graft testing
 graft doc
 
@@ -29,6 +32,3 @@ exclude appveyor
 
 exclude ISSUES.txt
 exclude HOWTORELEASE.rst
-exclude plugin-test.sh
-exclude requirements-docs.txt
-exclude runtox.py