Python :  pip install requestsで失敗する件のエラー解消方法

### 『エラー現状』
python内で、『requests』をimportするためにrequestsモジュールをpipで、installする際に下のエラーがでることがあります。
pythonのバージョンは、2.7です。

```shell-session
$ pip install requests
Collecting requests
  Could not fetch URL https://pypi.python.org/simple/requests/: There was a problem confirming the ssl certificate: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:590) - skipping
  Could not find a version that satisfies the requirement requests (from versions: )
No matching distribution found for requests
```
どうやら、ssl証明書あたりでエラーを履いているようです。


### 『解消方法』
解消方法は簡単で、pipをアップデートすれば直ります。

```shell-session
$ curl https://bootstrap.pypa.io/get-pip.py | python
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 1604k  100 1604k    0     0  1375k      0  0:00:01  0:00:01 --:--:-- 1375k
Collecting pip
  Downloading https://files.pythonhosted.org/packages/5f/25/e52d3f31441505a5f3af41213346e5b6c221c9e086a166f3703d2ddaf940/pip-18.0-py2.py3-none-any.whl (1.3MB)
    100% |████████████████████████████████| 1.3MB 2.7MB/s 
Collecting wheel
  Downloading https://files.pythonhosted.org/packages/81/30/e935244ca6165187ae8be876b6316ae201b71485538ffac1d718843025a9/wheel-0.31.1-py2.py3-none-any.whl (41kB)
    100% |████████████████████████████████| 51kB 3.0MB/s 
Installing collected packages: pip, wheel
  Found existing installation: pip 8.1.1
    Uninstalling pip-8.1.1:
      Successfully uninstalled pip-8.1.1
Successfully installed pip-18.0 wheel-0.31.1
```

再度、『pip install requests』実行

```shell-session
sh-3.2# pip install requests
Collecting requests
  Downloading https://files.pythonhosted.org/packages/65/47/7e02164a2a3db50ed6d8a6ab1d6d60b69c4c3fdf57a284257925dfc12bda/requests-2.19.1-py2.py3-none-any.whl (91kB)
    100% |████████████████████████████████| 92kB 2.1MB/s 
Collecting idna<2.8,>=2.5 (from requests)
  Downloading https://files.pythonhosted.org/packages/4b/2a/0276479a4b3caeb8a8c1af2f8e4355746a97fab05a372e4a2c6a6b876165/idna-2.7-py2.py3-none-any.whl (58kB)
    100% |████████████████████████████████| 61kB 3.1MB/s 
Collecting urllib3<1.24,>=1.21.1 (from requests)
  Downloading https://files.pythonhosted.org/packages/bd/c9/6fdd990019071a4a32a5e7cb78a1d92c53851ef4f56f62a3486e6a7d8ffb/urllib3-1.23-py2.py3-none-any.whl (133kB)
    100% |████████████████████████████████| 143kB 3.8MB/s 
Collecting chardet<3.1.0,>=3.0.2 (from requests)
  Downloading https://files.pythonhosted.org/packages/bc/a9/01ffebfb562e4274b6487b4bb1ddec7ca55ec7510b22e4c51f14098443b8/chardet-3.0.4-py2.py3-none-any.whl (133kB)
    100% |████████████████████████████████| 143kB 2.4MB/s 
Collecting certifi>=2017.4.17 (from requests)
  Downloading https://files.pythonhosted.org/packages/7c/e6/92ad559b7192d846975fc916b65f667c7b8c3a32bea7372340bfe9a15fa5/certifi-2018.4.16-py2.py3-none-any.whl (150kB)
    100% |████████████████████████████████| 153kB 3.5MB/s 
Installing collected packages: idna, urllib3, chardet, certifi, requests
Successfully installed certifi-2018.4.16 chardet-3.0.4 idna-2.7 requests-2.19.1 urllib3-1.23
```

無事成功しました。


参考 : [Problem Confirming the SSL Certificate - OSX · Issue #5236 · pypa/pip](https://github.com/pypa/pip/issues/5236)