Switch to assert=plain; apparently assert=reinterp is no longer supported

.travis.yml

@@ -143,7 +143,7 @@ script:
 
     # Run unit tests
     - start_test "unit tests";
-      PYTHONPATH=. py.test --cov --assert=reinterp pyqtgraph -sv;
+      PYTHONPATH=. py.test --cov --assert=plain pyqtgraph -sv;
       check_output "unit tests";
     - echo "test script finished. Current directory:"
     - pwd

pyqtgraph/tests/test_reload.py

@@ -57,7 +57,7 @@ def test_reload():
     if oldcfn is None:
         # Function did not reload; are we using pytest's assertion rewriting?
         raise Exception("Function did not reload. (This can happen when using py.test"
-            " with assertion rewriting; use --assert=reinterp or --assert=plain)")
+            " with assertion rewriting; use --assert=plain for this test.)")
     assert oldcfn.im_class is v1[0]
     assert oldcfn.im_func is v1[2].im_func
     assert oldcfn.im_self is c