Fix gate

and a related script.

pydot2 is not maintained and stopped being installable.
pydot is maintained and seems to work the same.

Change-Id: Id248d2349c31b4cb4ad82c2afde10787c75081c7

requirements.txt

@@ -1,7 +1,7 @@
 # NOTE(harlowja): For graph generation tool.
 #
 # Not currently needed for anything else.
-pydot2>=1.0.32
+pydot
 PyYAML>=3.1.0
 six>=1.9.0
 yamlordereddictloader

tools/universe_dot.py

@@ -138,5 +138,5 @@ end = time.time()
 print("Finished in %0.2f seconds" % (end - start))
 
 print("Writing graph to '%s'" % output_dot_file)
-with open(output_dot_file, "wb") as fh:
+with open(output_dot_file, "w") as fh:
     fh.write(graph.to_string())