プロキシあるJupyter環境で外部データを取ってくる

### やりたいこと
会社のプロキシがある環境で、Kerasデータセットのミニストを取りたかった。

```
import tensorflow as tf

# MNISTデータセットをロード
(x_train, y_train), (x_test, y_test) = tf.keras.datasets.mnist.load_data()
```

### エラー発生
```ValueError                                Traceback (most recent call last)
/usr/lib/python3.6/http/client.py in _get_hostport(self, host, port)
    904                 try:
--> 905                     port = int(host[i+1:])
    906                 except ValueError:

ValueError: invalid literal for int() with base 10: 'port'

During handling of the above exception, another exception occurred:

InvalidURL                                Traceback (most recent call last)
<ipython-input-8-8d03e8f41e48> in <module>
     17     include_top = False,
     18     weights = "imagenet",
---> 19     input_shape = None)
     20 
     21     x = base_model.output

/usr/local/lib/python3.6/dist-packages/keras/applications/xception.py in Xception(include_top, weights, input_tensor, input_shape, pooling, classes, classifier_activation)
    307           TF_WEIGHTS_PATH_NO_TOP,
    308           cache_subdir='models',
--> 309           file_hash='b0042744bf5b25fce3cb969f33bebb97')
    310     model.load_weights(weights_path)
    311   elif weights is not None:

/usr/local/lib/python3.6/dist-packages/keras/utils/data_utils.py in get_file(fname, origin, untar, md5_hash, file_hash, cache_subdir, hash_algorithm, extract, archive_format, cache_dir)
    272     try:
    273       try:
--> 274         urlretrieve(origin, fpath, dl_progress)
    275       except urllib.error.HTTPError as e:
    276         raise Exception(error_msg.format(origin, e.code, e.msg))

/usr/local/lib/python3.6/dist-packages/keras/utils/data_utils.py in urlretrieve(url, filename, reporthook, data)
     80           break
     81 
---> 82     response = urlopen(url, data)
     83     with open(filename, 'wb') as fd:
     84       for chunk in chunk_read(response, reporthook=reporthook):

/usr/lib/python3.6/urllib/request.py in urlopen(url, data, timeout, cafile, capath, cadefault, context)
    221     else:
    222         opener = _opener
--> 223     return opener.open(url, data, timeout)
    224 
    225 def install_opener(opener):

/usr/lib/python3.6/urllib/request.py in open(self, fullurl, data, timeout)
    524             req = meth(req)
    525 
--> 526         response = self._open(req, data)
    527 
    528         # post-process response

/usr/lib/python3.6/urllib/request.py in _open(self, req, data)
    542         protocol = req.type
    543         result = self._call_chain(self.handle_open, protocol, protocol +
--> 544                                   '_open', req)
    545         if result:
    546             return result

/usr/lib/python3.6/urllib/request.py in _call_chain(self, chain, kind, meth_name, *args)
    502         for handler in handlers:
    503             func = getattr(handler, meth_name)
--> 504             result = func(*args)
    505             if result is not None:
    506                 return result

/usr/lib/python3.6/urllib/request.py in https_open(self, req)
   1366         def https_open(self, req):
   1367             return self.do_open(http.client.HTTPSConnection, req,
-> 1368                 context=self._context, check_hostname=self._check_hostname)
   1369 
   1370         https_request = AbstractHTTPHandler.do_request_

/usr/lib/python3.6/urllib/request.py in do_open(self, http_class, req, **http_conn_args)
   1291 
   1292         # will parse host:port
-> 1293         h = http_class(host, timeout=req.timeout, **http_conn_args)
   1294         h.set_debuglevel(self._debuglevel)
   1295 

/usr/lib/python3.6/http/client.py in __init__(self, host, port, key_file, cert_file, timeout, source_address, context, check_hostname)
   1411                      check_hostname=None):
   1412             super(HTTPSConnection, self).__init__(host, port, timeout,
-> 1413                                                   source_address)
   1414             if (key_file is not None or cert_file is not None or
   1415                         check_hostname is not None):

/usr/lib/python3.6/http/client.py in __init__(self, host, port, timeout, source_address)
    865         self._tunnel_headers = {}
    866 
--> 867         (self.host, self.port) = self._get_hostport(host, port)
    868 
    869         self._validate_host(self.host)

/usr/lib/python3.6/http/client.py in _get_hostport(self, host, port)
    908                         port = self.default_port
    909                     else:
--> 910                         raise InvalidURL("nonnumeric port: '%s'" % host[i+1:])
    911                 host = host[:i]
    912             else:

InvalidURL: nonnumeric port: 'port' 
```

### 解決方法
環境に設定してあげれば解決。

```
import os

os.environ["HTTP_PROXY"] = "http://10.13x.x.6:80xx"
os.environ["HTTPS_PROXY"] = "http://10.13x.x.6:80xx"

os.environ["https_proxy"] = "http://10.13x.x.6:80xx"
os.environ["http_proxy"] = "http://10.13x.x.6:80xx"
```