fix(tests): use py3.6-compatible subprocess.run kwargs

capture_output and text were added in Python 3.7; CI runs 3.6, so
TestTokenTableGenerators failed with TypeError on every case before
the test body ran.

Author: BitHighlander

tests/test_token_table_generators.py

@@ -56,7 +56,8 @@ def _run(self, script):
             out = os.path.join(tmp, 'out.def')
             proc = subprocess.run(
                 [sys.executable, os.path.join(_ETH, script), out],
-                capture_output=True, text=True, cwd=_PYKEEPKEY)
+                stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+                universal_newlines=True, cwd=_PYKEEPKEY)
             self.assertEqual(
                 proc.returncode, 0,
                 '%s exited %d -- the firmware build runs this exact command '