bpo-31231: Fix pythoninfo in Travis config (#3134)

bpo-31231, bpo-30871: Replace "./python -m test.pythoninfo" with
"make pythoninfo", since macOS uses ./python.exe.
diff --git a/.travis.yml b/.travis.yml
index 4c43124..f6e9057 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -88,7 +88,7 @@
         echo "$changes"
         exit 1
       fi
-      ./python -m test.pythoninfo
+      make pythoninfo
 
 script:
   # Using the built Python as patchcheck.py is built around the idea of using