Dockerfile: set LANG env var to prevent encoding errors
Dockerfile: set LANG env var to prevent encoding errors

Specifically to fix this error in examples/urlopen.mochi:

$ mochi /files/examples/urlopen.mochi
Traceback (most recent call last):
  File "/venv/mochi/lib/python3.4/site-packages/eventlet/hubs/poll.py", line 115, in wait
    listener.cb(fileno)
  File "/venv/mochi/lib/python3.4/site-packages/eventlet/greenthread.py", line 214, in main
    result = function(*args, **kwargs)
  File "/venv/mochi/lib/python3.4/site-packages/mochi/actor/actor.py", line 175, in run
    self._callback(*args, **kwargs)
  File "/files/examples/urlopen.mochi", line 21, in fetch
    url: read(url)
  File "/files/examples/urlopen.mochi", line 13, in read
    print(weather['title'])
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-3: ordinal not in range(128)

i2y/mochi,slideclick/mochi,slideclick/mochi,pya/mochi,pya/mochi,i2y/mochi