dest error for unicode

[vnitinv]

Description of Issue

root@iagent:/# salt '*' srx.cli "show xyz" dest="/var/tmp/nitin.log"
proxy01:
    The minion function caused an exception: Traceback (most recent call last):
      File "/usr/local/lib/python3.6/dist-packages/salt/metaproxy/proxy.py", line 397, in thread_return
        return_data = minion_instance.executors[fname](opts, data, func, args, kwargs)
      File "/usr/local/lib/python3.6/dist-packages/salt/executors/direct_call.py", line 12, in execute
        return func(*args, **kwargs)
      File "/var/cache/salt/proxy/extmods/proxy01/modules/srx.py", line 436, in cli
        fp.write(salt.utils.stringutils.to_str(result))
    UnicodeEncodeError: 'ascii' codec can't encode character '\xa0' in position 5346339: ordinal not in range(128)

Setup

(Please provide relevant configs and/or SLS files (Be sure to remove sensitive info).)

Steps to Reproduce Issue

(Include debug logs if possible and relevant.)

Versions Report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)