Fix 'ascii' codec can't encode character u'\u2716' when tern_show_arg…

[othree]

When I use show argument hint feature. I will see this error message.

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/othree/.vim/bundle/tern_for_vim/script/tern.py", line 318, in tern_lookupType
    if data: tern_echoWrap(data.get("type", ""))
  File "/Users/othree/.vim/bundle/tern_for_vim/script/tern.py", line 314, in tern_echoWrap
    vim.command("echo '{0}'".format(text))
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2716' in position 3: ordinal not in range(128)

The reason is the cross sign.

[marijnh]

Thanks! Merged as 8eb1451