update install doc in tests (#621)

diff --git a/dill/tests/__init__.py b/dill/tests/__init__.py
index e4e1bdc..c8837ea 100644
--- a/dill/tests/__init__.py
+++ b/dill/tests/__init__.py
@@ -7,8 +7,7 @@
 """
 to run this test suite, first build and install `dill`.
 
-  $ python setup.py build
-  $ python setup.py install
+  $ python -m pip install ../..
 
 
 then run the tests with: