Print versions of software used in Travis output

tools/build_versions.py

@@ -0,0 +1,12 @@
+#!/usr/bin/env python
+
+from __future__ import print_function
+
+import numpy as np
+import scipy as sp
+import matplotlib as mpl
+import six
+
+for m in (np, sp, mpl, six):
+    print(m.__name__.rjust(10), ' ', m.__version__)
+