Fix python3 parsing of subprocess output

As described in the python docs, use "universal_newlines" to
subprocess so the output are text streams.

With this, tox -e py34 works

Change-Id: I79091ed98054f25414d99824ee686bdf38ab968e

bashate/bashate.py

@@ -173,7 +173,8 @@ def check_syntax(filename, report):
     bash_environment['LC_ALL'] = 'C'
     proc = subprocess.Popen(
         ['bash', '-n', filename], stdout=subprocess.PIPE,
-        stderr=subprocess.PIPE, env=bash_environment)
+        stderr=subprocess.PIPE, env=bash_environment,
+        universal_newlines=True)
     outputs = proc.communicate()
 
     for line in outputs[1].split('\n'):